SCHEDULE 14A INFORMATION
 
                  Proxy Statement Pursuant to Section 14(a) of
                      the Securities Exchange Act of 1934
 
    Filed by the registrant /X/
    Filed by a Party other than the Registrant / /
 
    Check the appropriate box:
    / /  Preliminary Proxy Statement
    / /  Confidential, for Use of the Commission Only (as permitted by Rule
         14a-6(e)(2))
    /X/  Definitive Proxy Statement
    / /  Definitive Additional Materials
    / /  Soliciting Material Pursuant to Rule 14a-11(c) or Rule 14a-12
 
                               AFFILIATED MANAGERS GROUP, INC.
- - --------------------------------------------------------------------------------
                (Name of Registrant as Specified In Its Charter)
 
- - --------------------------------------------------------------------------------
    (Name of Person(s) Filing Proxy Statement, if other than the Registrant)
 
Payment of filing fee (Check the appropriate box):
 
/X/  No fee required.
/ /  Fee computed on table below per Exchange Act Rules 14a-6(i)(4)
     and 0-11.
     (1) Title of each class of securities to which transaction applies:
         -----------------------------------------------------------------------
     (2) Aggregate number of securities to which transaction applies:
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     (3) Per unit price or other underlying value of transaction computed
         pursuant to Exchange Act Rule 0-11:
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     (5) Total fee paid:
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/ /  Fee paid previously with preliminary materials.
/ /  Check box if any part of the fee is offset as provided by Exchange Act Rule
     0-11(a)(2) and identify the filing for which the offsetting fee was paid
     previously. Identify the previous filing by registration statement number,
     or the form or schedule and the date of its filing.
     (1) Amount Previously Paid:
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                        AFFILIATED MANAGERS GROUP, INC.
 
                      TWO INTERNATIONAL PLACE, 23RD FLOOR
                          BOSTON, MASSACHUSETTS 02110
 
                            ------------------------
 
                    NOTICE OF ANNUAL MEETING OF STOCKHOLDERS
                           TO BE HELD ON MAY 25, 1999
 
                            ------------------------
 
    NOTICE IS HEREBY GIVEN that the 1999 Annual Meeting of Stockholders (the
"Annual Meeting") of Affiliated Managers Group, Inc. ("AMG" or the "Company")
will be held on Tuesday, May 25, 1999 at 9:00 a.m. Boston time at the offices of
Goodwin, Procter & Hoar LLP at Exchange Place, 53 State Street, Boston,
Massachusetts 02109 for the following purposes:
 
    1. To elect six directors of the Company to serve until the 2000 Annual
Meeting of Stockholders and until their respective successors are duly elected
and qualified.
 
    2. To consider and act upon a proposal to approve the amendment and
restatement of the Company's 1997 Stock Option and Incentive Plan.
 
    3. To consider and act upon any other matters that may properly be brought
before the Annual Meeting and at any adjournments or postponements thereof.
 
    Any action may be taken on the foregoing matters at the Annual Meeting on
the date specified above, or on any date or dates to which, by original or later
adjournment, the Annual Meeting may be adjourned, or to which the Annual Meeting
may be postponed.
 
    The Board of Directors has fixed the close of business on March 31, 1999 as
the record date for determining the stockholders entitled to notice of and to
vote at the Annual Meeting and at any adjournments or postponements thereof.
Only stockholders of record of the Company's common stock, par value $.01 per
share (the "Common Stock"), at the close of business on that date will be
entitled to notice of the Annual Meeting. Only stockholders of record of voting
Common Stock at the close of business on that date will be entitled to vote at
the Annual Meeting and at any adjournments or postponements thereof.
 
    You are requested to fill in and sign the enclosed form of proxy, which is
being solicited by the Board of Directors of the Company, and to mail it
promptly in the enclosed postage-prepaid envelope. Any proxy may be revoked by
delivery of a later dated proxy. Stockholders of record who attend the Annual
Meeting may vote in person, even if they have previously delivered a signed
proxy.
 
                                        By Order of the Board of Directors
 
                                                      [LOGO]
 
                                        Nathaniel Dalton
 
                                        SECRETARY
 
Boston, Massachusetts
April 23, 1999
 
    WHETHER OR NOT YOU PLAN TO ATTEND THE ANNUAL MEETING, PLEASE COMPLETE, SIGN,
DATE AND PROMPTLY RETURN THE ENCLOSED PROXY CARD IN THE POSTAGE-PREPAID ENVELOPE
PROVIDED. IF YOU ARE A STOCKHOLDER OF RECORD AND YOU ATTEND THE ANNUAL MEETING,
YOU MAY VOTE IN PERSON IF YOU WISH, EVEN IF YOU HAVE PREVIOUSLY RETURNED YOUR
PROXY CARD.

                        AFFILIATED MANAGERS GROUP, INC.
 
                      TWO INTERNATIONAL PLACE, 23RD FLOOR
                          BOSTON, MASSACHUSETTS 02110
 
                            ------------------------
 
                                PROXY STATEMENT
 
                            ------------------------
 
                       FOR ANNUAL MEETING OF STOCKHOLDERS
                           TO BE HELD ON MAY 25, 1999
 
                                                                  April 23, 1999
 
    This Proxy Statement is furnished in connection with the solicitation of
proxies by the Board of Directors of Affiliated Managers Group, Inc. ("AMG" or
the "Company") for use at the 1999 Annual Meeting of Stockholders of the Company
to be held on Tuesday, May 25, 1999 at 9:00 a.m. Boston time at the offices of
Goodwin, Procter & Hoar LLP at Exchange Place, 53 State Street, Boston,
Massachusetts, 02109, and at any adjournments or postponements thereof (the
"Annual Meeting"). At the Annual Meeting, stockholders will be asked to vote
upon the election of six directors of the Company, to consider and act upon a
proposal to approve the amendment and restatement of the Company's 1997 Stock
Option and Incentive Plan (the "1997 Stock Plan"), and to act upon any other
matters properly brought before them.
 
    This Proxy Statement and the accompanying Notice of Annual Meeting and Proxy
Card are first being sent to stockholders on or about April 23, 1999. The Board
of Directors has fixed the close of business on March 31, 1999 as the record
date for the determination of stockholders entitled to notice of and to vote at
the Annual Meeting (the "Record Date"). Only stockholders of record of the
Company's common stock, par value $.01 per share (the "Common Stock"), at the
close of business on the Record Date will be entitled to notice of the Annual
Meeting. Only stockholders of record of voting Common Stock at the close of
business on the Record Date will be entitled to vote at the Annual Meeting.
Holders of Common Stock outstanding and entitled to vote as of the close of
business on the Record Date will be entitled to one vote for each share held by
them. As of the Record Date, there were 21,790,480 shares of Common Stock
outstanding and entitled to vote at the Annual Meeting.
 
    The presence, in person or by proxy, of holders of at least a majority of
the total number of shares of Common Stock outstanding and entitled to vote is
necessary to constitute a quorum for the transaction of business at the Annual
Meeting. Both abstentions and broker non-votes (as defined below) will be
counted as present in determining the presence of a quorum. A plurality of votes
cast shall be sufficient for the election of directors. Abstentions and broker
non-votes will be disregarded in determining the "votes cast" for purposes of
electing directors and will not affect the election of the candidates receiving
a plurality of votes. The affirmative vote of the holders of a majority of the
shares of Common Stock present or represented and entitled to vote is required
to approve the amendment and restatement of the 1997 Stock Plan (the "Plan
Amendment"). Abstentions will be included in determining the number of shares of
Common Stock present or represented and entitled to vote for purposes of
approval of the Plan Amendment, and will therefore have the effect of votes
"against" the proposal. Broker non-votes will not be counted in determining the
number of shares of Common Stock present or represented and entitled to vote to
approve the Plan Amendment, and will therefore not have the effect of votes
either "for" or "against" the proposal. A "broker non-vote" is a proxy from a
broker or other nominee indicating that such person has not received
instructions from the beneficial owner or other person entitled to vote the
shares which are the subject of the proxy on a particular matter with respect to
which the broker or other nominee does not have discretionary voting power.
 
                                       1

    STOCKHOLDERS OF THE COMPANY ARE REQUESTED TO COMPLETE, SIGN, DATE AND
PROMPTLY RETURN THE ACCOMPANYING PROXY CARD IN THE ENCLOSED, POSTAGE-PREPAID
ENVELOPE. SHARES REPRESENTED BY A PROPERLY EXECUTED PROXY RECEIVED PRIOR TO THE
VOTE AT THE ANNUAL MEETING AND NOT REVOKED WILL BE VOTED AT THE ANNUAL MEETING
AS DIRECTED ON THE PROXY. IF A PROPERLY EXECUTED PROXY IS SUBMITTED AND NO
INSTRUCTIONS ARE GIVEN, THE PROXY WILL BE VOTED FOR THE ELECTION OF THE NOMINEES
FOR DIRECTOR OF THE COMPANY NAMED IN THIS PROXY STATEMENT AND FOR THE PROPOSAL
TO APPROVE THE PLAN AMENDMENT. IT IS NOT ANTICIPATED THAT ANY MATTERS OTHER THAN
THOSE SET FORTH IN THIS PROXY STATEMENT WILL BE PRESENTED AT THE ANNUAL MEETING.
IF OTHER MATTERS ARE PRESENTED, PROXIES WILL BE VOTED IN ACCORDANCE WITH THE
DISCRETION OF THE PROXY HOLDERS.
 
    A stockholder of record may revoke a proxy at any time before it has been
exercised by filing a written revocation with the Secretary of the Company at
the address of the Company set forth above; by filing a duly executed proxy
bearing a later date; or by appearing in person and voting by ballot at the
Annual Meeting. Any stockholder of record as of the Record Date attending the
Annual Meeting may vote in person whether or not a proxy has previously been
given, but the presence (without further action) of a stockholder at the Annual
Meeting will not constitute revocation of a previously given proxy.
 
    The Company's 1998 Annual Report, including audited financial statements for
the fiscal year ended December 31, 1998, is being mailed to stockholders
concurrently with this Proxy Statement. The Annual Report, however, is not part
of the proxy solicitation materials.
 
                       PROPOSAL 1: ELECTION OF DIRECTORS
 
INTRODUCTION
 
    The Board of Directors of the Company consists of six members. At the Annual
Meeting, six directors will be elected to serve until the 2000 Annual Meeting of
Stockholders and until their respective successors are duly elected and
qualified. The Board of Directors has nominated William J. Nutt, Richard E.
Floor, P. Andrews McLane, John M. B. O'Connor, W. W. Walker, Jr. and William F.
Weld (the "Nominees") to serve as directors. Each of the Nominees is currently
serving as a director of the Company. The Board of Directors anticipates that
each of the Nominees will serve, if elected, as a director. However, if any
person nominated by the Board of Directors is unable to accept election, the
proxies will be voted for the election of such other person or persons as the
Board of Directors may recommend. The Board of Directors will consider a nominee
for election to the Board of Directors recommended by a stockholder of record if
the stockholder submits the nomination in compliance with the requirements of
the Company's Amended and Restated By-laws (the "By-laws"). See "Other
Matters--Stockholder Proposals" for a summary of these requirements.
 
RECOMMENDATION
 
    THE BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS A VOTE FOR EACH OF THE
NOMINEES.
 
                                       2

INFORMATION REGARDING THE DIRECTORS/NOMINEES
 
    The names, ages and a description of the business experience, principal
occupation and past employment during at least the last five years of each of
the Nominees are set forth below.
 


NAME                                                                                          AGE
- - ----------------------------------------------------------------------------------------      ---
                                                                                       
William J. Nutt(2)......................................................................          54
Richard E. Floor(1).....................................................................          58
P. Andrews McLane(2)....................................................................          51
John M. B. O'Connor(2)..................................................................          44
W. W. Walker, Jr.(1)....................................................................          51
William F. Weld(1)......................................................................          53

 
- - ------------------------
 
(1) Member of the Audit Committee.
 
(2) Member of the Compensation Committee.
 
    WILLIAM J. NUTT founded the Company in December 1993 and has served as its
Chairman, Chief Executive Officer and President since that time. Mr. Nutt began
his career at the law firm of Ballard, Spahr, Andrews & Ingersoll in
Philadelphia, where he was a Partner until he joined The Boston Company in 1982.
As Senior Executive Vice President of that firm, Mr. Nutt built The Boston
Company's mutual fund administration, distribution and custody business serving
over 45 fund sponsors with assets of $119.0 billion. In 1989, he became
President, assuming overall responsibility for The Boston Company's $36.0
billion institutional money management business, its $190.0 billion master
trustee and custodian business, and the personal banking and trust business of
the Boston Safe Deposit and Trust Company. Mr. Nutt received a J.D. from the
University of Pennsylvania and a B.A. from Grove City College. From 1991 to
1994, Mr. Nutt served on the Executive Committee of the Board of Governors of
the Investment Company Institute.
 
    RICHARD E. FLOOR has been a director of the Company since its formation. A
professional corporation of which Mr. Floor is the sole stockholder is and has
been a senior partner at the law firm of Goodwin, Procter & Hoar LLP or its
predecessor since 1975. Mr. Floor is also a director of New America High Income
Fund, a closed-end investment company.
 
    P. ANDREWS MCLANE has been a director of the Company since its formation.
Since 1979, he has been associated with TA Associates, Inc. or its predecessors,
where he is Senior Managing Director and a member of the firm's Executive
Committee. Mr. McLane leads TA Associates' investment activities in the asset
management industry. Mr. McLane is also a director of Allegis Realty Investors,
LLC, Altamira Investment Services, Inc., Natrol, Inc., and United Pet Group,
Inc.
 
    JOHN M. B. O'CONNOR has been a director of the Company since October 1997.
Mr. O'Connor is a General Partner of Chase Capital Partners, which he joined in
May 1995. Mr. O'Connor has been employed by Chase Manhattan Corporation or its
predecessors since 1987 in a variety of senior investment banking positions
including management of Corporate Securities Sales, Trading and Research. Mr.
O'Connor is also a director of FHC Health Systems, Inc., a behavioral healthcare
company.
 
    W. W. WALKER, JR. has been a director of the Company since April 1997. Since
1972, Mr. Walker has been employed by NationsBank, N.A. or its predecessor,
where he has held positions in various departments including corporate banking,
private placements, syndications and project finance. Mr. Walker founded Bank of
America Capital Investors in 1993 and is presently Senior Managing Director of
that group.
 
    WILLIAM F. WELD has been a director of the Company since December 1997. Mr.
Weld is a Partner in the law firm of McDermott, Will & Emery. From 1991 to 1997,
Mr. Weld served as the Governor of Massachusetts. His prior experience includes
two years as Assistant U.S. Attorney General, Criminal
 
                                       3

Division, and five years as the United States Attorney for Massachusetts. Mr.
Weld has also previously been engaged in the private practice of law at Hill &
Barlow and Hale and Dorr. Mr. Weld is also a director of NovaCare Employee
Services, Inc.
 
    During 1998, the Board of Directors met 11 times. During 1998, each director
attended at least 75% of the aggregate of (i) the total number of meetings of
the Board of Directors (held during the period for which such director served on
the Board of Directors) and (ii) the total number of meetings of all committees
of the Board of Directors on which such director served (during the periods for
which such director served on such committee or committees).
 
    The Board of Directors has established an Audit Committee (the "Audit
Committee") and a Compensation Committee (the "Compensation Committee"). The
Audit Committee recommends the firm to be appointed as independent accountants
to audit financial statements and to perform services related to the audit,
reviews the scope and results of the audit with the independent accountants,
reviews with management and the independent accountants the Company's operating
results, considers the adequacy of internal accounting procedures and considers
the effect of such procedures on the accountants' independence. The Audit
Committee currently consists of Messrs. Floor, Walker and Weld. The Audit
Committee met four times during 1998. The Compensation Committee, which
currently consists of Messrs. Nutt, McLane and O'Connor, reviews and recommends
the compensation arrangements for all directors and officers, except that Mr.
Nutt does not participate in the recommendation of his compensation
arrangements. The Compensation Committee met four times during 1998. The Board
of Directors does not have a standing nominating committee. The full Board of
Directors performs the function of such a committee.
 
COMPENSATION OF DIRECTORS
 
    Directors of the Company who are also employees receive no additional
compensation for their service as directors. Messrs. Floor and Weld each receive
an annual fee of $16,000 for their services as a director. In addition, Messrs.
Floor and Weld each receive $2,000 for each Board of Directors' meeting
personally attended and $1,000 for each Board meeting attended via
tele-conference. Non-employee directors are also eligible to receive options to
purchase shares of Common Stock under the Affiliated Managers Group, Inc. 1997
Stock Option and Incentive Plan (the "Plan").
 
    All directors of the Company are reimbursed for travel expenses incurred in
attending meetings of the Board of Directors and its committees.
 
INFORMATION REGARDING EXECUTIVE OFFICERS
 
    The names, ages and positions of each of the executive officers of the
Company, as well as a description of their business experience and past
employment, are as set forth below:
 


NAME                                                       AGE                            POSITION
- - -----------------------------------------------------      ---      -----------------------------------------------------
                                                              
William J. Nutt......................................          54   Chairman, Chief Executive Officer and President
Sean M. Healey.......................................          37   Executive Vice President
Levon Chertavian, Jr.................................          39   Senior Vice President, Affiliate Support
Darrell W. Crate.....................................          32   Senior Vice President, Chief Financial Officer and
                                                                      Treasurer
Nathaniel Dalton.....................................          32   Senior Vice President, General Counsel and Secretary
Seth W. Brennan......................................          28   Vice President
Jeffrey S. Murphy....................................          32   Vice President
Daniel J. Shea.......................................          33   Vice President

 
    For Mr. Nutt's biographical information, see "--Information Regarding the
Directors/Nominees."
 
                                       4

    SEAN M. HEALEY joined the Company as its Executive Vice President in 1995.
Prior to joining AMG, Mr. Healey was a Vice President in the Mergers and
Acquisitions Department at Goldman, Sachs & Co. focusing on financial
institutions. In eight years at Goldman Sachs, Mr. Healey had substantial
experience advising clients and executing transactions in the investment
management and related industries. Mr. Healey received a J.D. from Harvard Law
School, an M.A. from University College, Dublin and an A.B. from Harvard
College.
 
    LEVON CHERTAVIAN, JR. joined the Company as Senior Vice President, Affiliate
Support in 1995. Mr. Chertavian was formerly President of USAffinity Advisers,
the mutual fund operation of TransNational Group. Prior to TransNational Group,
Mr. Chertavian held positions with Bain & Company, Fidelity Investments, Bankers
Trust Company and Equitable Life. Mr. Chertavian received an M.B.A. from the
Harvard Business School and a B.A. from Bowdoin College.
 
    DARRELL W. CRATE joined the Company as a Senior Vice President and Chief
Financial Officer in 1998. Prior to joining AMG, Mr. Crate was a Managing
Director with Chase Securities, Inc. Mr. Crate received an M.B.A. from Columbia
Business School and a B.A. from Bates College.
 
    NATHANIEL DALTON joined the Company as a Senior Vice President and General
Counsel in 1996. Prior to joining AMG, Mr. Dalton was an attorney at Goodwin,
Procter & Hoar LLP, focusing on mergers and acquisitions, including those in the
asset management industry. Mr. Dalton received a J.D. from Boston University
School of Law and a B.A. from the University of Pennsylvania.
 
    SETH W. BRENNAN joined the Company as an Assistant Vice President in 1995,
and became a Vice President in 1996. Prior to joining AMG, Mr. Brennan was a
Financial Analyst in the Global Insurance Investment Banking Group at Morgan
Stanley & Co. Incorporated. Before joining Morgan Stanley, Mr. Brennan was a
Financial Analyst in the Financial Institutions Group at Wasserstein, Perella &
Co. Mr. Brennan received a B.A. from Hamilton College.
 
    JEFFREY S. MURPHY joined the Company as an Assistant Vice President in 1995,
and became a Vice President in 1996. Prior to joining AMG, Mr. Murphy was a
Financial Analyst at United Asset Management Corporation, and prior to that, Mr.
Murphy was the Assistant Controller of TA Associates, Inc. Mr. Murphy received a
B.S. in Business Administration from Northeastern University.
 
    DANIEL J. SHEA joined the Company as a Vice President in 1998. Prior to
joining AMG, Mr. Shea was a Senior Manager in the Financial Services Group of
Coopers & Lybrand L.L.P. Mr. Shea received a B.S. in Accounting and Finance from
Boston College and is a Certified Public Accountant.
 
EXECUTIVE COMPENSATION
 
    SUMMARY COMPENSATION TABLE.  The following table sets forth information
concerning the cash compensation earned during the indicated periods by the
Company's Chief Executive Officer and the Company's four (4) other most highly
compensated executive officers whose total salary and bonus exceeded $100,000
during the fiscal year ended December 31, 1998 (collectively, the "Named
Executive Officers").
 
                                       5

                            SUMMARY OF COMPENSATION
 


                                                                         LONG TERM
                                                                        COMPENSATION
                                                                           AWARDS
                                                                        ------------
                                               ANNUAL COMPENSATION       SECURITIES
                                             ------------------------    UNDERLYING         ALL OTHER
NAME AND PRINCIPAL POSITION        YEAR      SALARY ($)     BONUS ($)   OPTIONS (#)     COMPENSATION ($)
- - --------------------------------- ------     ----------     ---------   ------------   -------------------
                                                                        
William J. Nutt, Chairman........   1998       462,500       575,000      82,500            28,200(1)
 President and Chief                1997       379,140       435,000     205,000            28,250(2)
 Executive Officer                  1996       345,350       315,000          --            26,750(3)
 
Sean M. Healey...................   1998       362,500       450,000      75,000            28,200(1)
 Executive Vice President           1997       301,920       350,000     195,000            28,250(2)
                                    1996       270,460       277,500          --            26,750(3)
 
Levon Chertavian, Jr.............   1998       200,000       175,000      42,500            27,432(1)
 Senior Vice President              1997       176,209       140,000      40,000            26,313(2)
                                    1996       159,227       116,667          --            24,813(3)
 
Darrell W. Crate.................   1998(4)    159,375       275,000     140,000            25,946(1)
 Senior Vice President
 
Nathaniel Dalton.................   1998       225,000       300,000      65,500            27,792(1)
 Senior Vice President              1997       176,371       190,000      72,500            26,313(2)
                                    1996(5)     98,498       100,000          --            17,068(3)

 
- - ------------------------
 
(1) Includes (i) contributions by the Company under its 401(k) Profit Sharing
    Plan in the amount of $24,000 on behalf of Messrs. Nutt, Healey, Chertavian
    and Dalton and $23,906 on behalf of Mr. Crate; and (ii) the dollar value of
    insurance premiums paid by the Company with respect to term life and long
    term disability insurance policies for the benefit of the Named Executive
    Officers in the amount of $4,200 on behalf of each of Messrs. Nutt and
    Healey, $3,792 on behalf of Mr. Dalton, $3,432 on behalf of Mr. Chertavian
    and $2,040 on behalf of Mr. Crate.
 
(2) Includes (i) contributions by the Company under its 401(k) Profit Sharing
    Plan in the amount of $24,000 on behalf of Messrs. Nutt, Healey, Chertavian
    and Dalton; and (ii) the dollar value of insurance premiums paid by the
    Company with respect to term life and long term disability insurance
    policies for the benefit of the Named Executive Officers in the amount of
    $4,250 on behalf of each of Messrs. Nutt and Healey and $2,313 on behalf of
    each of Messrs. Chertavian and Dalton.
 
(3) Includes (i) contributions by the Company under its 401(k) Profit Sharing
    Plan in the amount of $22,500 on behalf of each of Messrs. Nutt, Healey and
    Chertavian and $14,755 on behalf of Mr. Dalton; and (ii) the dollar value of
    insurance premiums paid by the Company with respect to term life and long
    term disability insurance policies for the benefit of the Named Executive
    Officers in the amount of $4,250 on behalf of each of Messrs. Nutt and
    Healey and $2,313 on behalf of each of Messrs. Chertavian and Dalton.
 
(4) Mr. Crate's employment with the Company commenced in April 1998.
 
(5) Mr. Dalton's employment with the Company commenced in May 1996.
 
                                       6

    OPTION GRANTS.
 
    The following table sets forth the option grants made during 1998 to the
Named Executive Officers.
 
                             OPTION GRANTS IN 1998
 


                                                   INDIVIDUAL GRANTS                        POTENTIAL REALIZABLE
                                -------------------------------------------------------       VALUE AT ASSUMED
                                               PERCENT OF                                     ANNUAL RATES OF
                                 NUMBER OF    TOTAL OPTIONS                                     STOCK PRICE
                                SECURITIES     GRANTED TO                                       APPRECIATION
                                UNDERLYING      EMPLOYEES     EXERCISE OR                    FOR OPTION TERM(1)
                                  OPTIONS       IN FISCAL     BASE PRICE    EXPIRATION   --------------------------
                                 GRANTED #        YEAR         ($/SHARE)       DATE         5% ($)       10% ($)
                                -----------  ---------------  -----------  ------------  ------------  ------------
                                                                                     
William J. Nutt...............     52,500(2)          9.8%     $   34.63       4/16/08   $  1,143,378  $  2,897,543
                                   30,000(3)          5.6%     $   27.69       12/3/08   $    522,423  $  1,323,922
 
Sean M. Healey................     47,500(2)          8.8%     $   34.63       4/16/08   $  1,034,484  $  2,621,587
                                   27,500(3)          5.1%     $   27.69       12/3/08   $    478,888  $  1,213,595
 
Levon Chertavian, Jr..........     30,000(2)          5.6%     $   34.63       4/16/08   $    653,359  $  1,655,739
                                   12,500(3)          2.3%     $   27.69       12/3/08   $    217,676  $    551,634
 
Darrell W. Crate..............    100,000(4)         18.6%     $   34.63       4/16/08   $  2,177,862  $  5,519,130
                                   40,000(3)          7.5%     $   27.69       12/3/08   $    696,564  $  1,765,229
 
Nathaniel Dalton..............     45,000(2)          8.4%     $   34.63       4/16/08   $    980,038  $  2,483,609
                                   20,500(3)          3.8%     $   27.69       12/3/08   $    356,989  $    904,680

 
- - ------------------------
 
(1) Amounts represent hypothetical gains that could be achieved for the
    respective options if exercised at the end of the option term. These gains
    are based upon assumed rates of stock appreciation set by the Securities and
    Exchange Commission (the "SEC") of five percent and ten percent compounded
    annually from the date the respective options were granted. Actual gains, if
    any, are dependent on the performance of the Common Stock. There can be no
    assurance that the amounts reflected will be achieved.
 
(2) Each of these options becomes exercisable over four years, with 25% becoming
    exercisable on each of the four calendar year ends after the date of the
    grant.
 
(3) Each of these options becomes exercisable over four years, with 25% becoming
    exercisable on each of the four calendar year ends beginning in the year
    following the date of grant.
 
(4) These options become exercisable over three years, with 25% exercisable on
    the date of grant and 25% becoming exercisable on each of the first three
    anniversaries of the date of grant.
 
                                       7

    YEAR-END OPTION HOLDINGS.  The following table sets forth the value of
options held at the end of 1998 by the Named Executive Officers. None of the
Named Executive Officers exercised any options during 1998.
 
                          1998 YEAR-END OPTION VALUES
 


                                               NUMBER OF                   VALUE OF
                                         SECURITIES UNDERLYING            UNEXERCISED
                                          UNEXERCISED OPTIONS        IN-THE-MONEY OPTIONS
                                            AT YEAR-END (#)             AT YEAR-END ($)
                                             EXERCISABLE /               EXERCISABLE /
                                             UNEXERCISABLE             UNEXERCISABLE(1)
                                        ------------------------  ---------------------------
                                                            
William J. Nutt.......................        56,792/230,708            $518,382/$1,214,043
Sean M. Healey........................        54,042/215,958            $508,819/$1,154,393
Levon Chertavian, Jr..................         18,667/63,833              $167,194/$259,118
Darrell W. Crate......................        25,000/115,000                     $0/$87,400
Nathaniel Dalton......................        29,875/108,125              $262,734/$460,246

 
- - ------------------------
 
(1) Based on $29.88 per share, the closing price of the Common Stock on the New
    York Stock Exchange on December 31, 1998.
 
STOCK PERFORMANCE GRAPH
 
    The following graph provides a comparison of cumulative total stockholder
return for the period from November 21, 1997 (the date on which the Common Stock
was first registered under Section 12 of the Securities Exchange Act of 1934, as
amended, and publicly traded) through December 31, 1998, among (i) the Company,
(ii) the Standard & Poor's 500 Stock Index (the "S&P 500 Index"); (iii) an
industry peer group index compiled by us that consists of the same companies
included in the industry peer group index shown in last year's proxy statement
("Old Peer Group"); and (iv) an industry peer group index compiled by us that
includes all of the public companies that we currently consider our peers ("New
Peer Group"). We developed the New Peer Group this year to include 1998 initial
public offerings and other peers with similar market capitalizations. The
companies included in the Old Peer Group and the New Peer Group are:
 


OLD PEER GROUP                                            NEW PEER GROUP
- - --------------------------------------------------------  --------------------------------------------------------
                                                       
Atalanta Sosnoff Capital Corp.                            Eaton Vance Corp.
Eaton Vance Corp.                                         Federated Investors, Inc.(1)
Franklin Resources, Inc.                                  Franklin Resources, Inc.
Liberty Financial Companies, Inc.                         John Nuveen & Co.
Phoenix Investment Partners, Ltd.                         Liberty Financial Companies, Inc.
The Pioneer Group, Inc.                                   Phoenix Investment Partners, Ltd.
T. Rowe Price Associates                                  The Pioneer Group, Inc.
United Asset Management                                   T. Rowe Price Associates
                                                          United Asset Management
                                                          Waddell & Reed Financial, Inc.(2)

 
(1) Included since its initial public offering in May 1998.
 
(2) Included since its initial public offering in March 1998.
 
                                       8

    SEC regulations require the Company to show all four indices this year, but
in the future the Company will cease using the Old Peer Group.
 
    The Stock Performance Graph assumes an investment of $100 in each of the
Company and the two indices, and the reinvestment of any dividends. The
historical information set forth below is not necessarily indicative of future
performance.
 
                     COMPARISON OF CUMULATIVE TOTAL RETURN*
           AMONG AFFILIATED MANAGERS GROUP, INC., THE S & P 500 INDEX
                                AND PEER GROUPS
 
EDGAR REPRESENTATION OF DATA POINTS USED IN PRINTED GRAPHIC
 


              ALLILIATED MANAGERS GROUP, INC.         OLD PEER GROUP        NEW PEER GROUP      S&P 500
                                                                                   
11/21/97                                      100                   100                   100        100
12/97                                         123                    96                    96        101
3/98                                          148                   113                   112        115
6/98                                          158                   113                   112        119
9/98                                           77                    74                    76        107
12/98                                         127                    81                    84        130

 

                                                                                        
                    * $100 INVESTED ON 11/21/97 IN STOCK OR INDEX -
                      INCLUDING REINVESTMENT OF DIVIDENDS.
                      FISCAL YEAR ENDING DECEMBER 31.

 
                                       9

                        COMPENSATION COMMITTEE REPORT ON
                             EXECUTIVE COMPENSATION
 
    The Compensation Committee of the Board of Directors consists of Mr. Nutt,
the Chairman, President and Chief Executive Officer of the Company, Mr. McLane
and Mr. O'Connor. The Compensation Committee is responsible for overseeing the
Company's general compensation policies and establishing and reviewing the
compensation plans applicable to the Company's executive officers. The
Compensation Committee's responsibilities include administering the Company's
stock option and incentive plans, although its actions with respect to such
plans are subject to the approval of the full Board of Directors.
 
    The Compensation Committee structures its policies and programs to further
the Company's basic philosophy that executive compensation should be closely
aligned with increases in stockholder value. In so doing, the Compensation
Committee closely monitors the allocation of the Company's executives'
compensation between salary, bonus and stock option grants so as to maintain an
appropriate balance between annual and performance-based compensation and to
create the optimum level of incentives for such executives to manage the
Company's affairs with the goal of increasing value to stockholders.
 
    In determining annual compensation levels for the Company's executive
officers, the Compensation Committee considers the Company's size and rate of
growth, performance as measured by the Company's earnings after interest expense
and income taxes but before depreciation and amortization and extraordinary
items ("EBITDA as adjusted") per share, earnings per share and assets under
management. The Compensation Committee also reviews the amounts of annual
compensation being paid to executive officers of other companies in the
industry, including those comprising the Peer Group Indices set forth on page 8.
Based on such reviews, the Compensation Committee believes that the annual
compensation opportunities provided to its executive officers (including Mr.
Nutt) are within the range of annual compensation opportunities offered by
comparable companies.
 
    In determining the performance-based compensation levels for the Company's
executive officers, the Compensation Committee considers, in addition to those
factors listed above, the performance of the applicable executive and the role
and level of responsibility such executive has assumed in the Company's
performance as a whole, the particular executive's importance to the future
growth of the Company, and the success of the particular executive individually
and collectively with the other members of the management team in achieving
short-term and long-term goals.
 
    In determining the annual and performance-based compensation levels for Mr.
Nutt, the Company's Chairman, Chief Executive Officer and President, the
Compensation Committee, without Mr. Nutt's participation, applies the same
principles and methods applied to other executive officers.
 
    The Compensation Committee and the Board of Directors as a whole considers
EBITDA as adjusted per share to be a particularly important basis for measuring
the value of the Company to its stockholders, and thus the Compensation
Committee places significant emphasis on EBITDA as adjusted per share in making
its compensation decisions. In 1998, the Compensation Committee determined that
performance-based compensation for the Company's officers which approximated
five percent of EBITDA as adjusted was appropriate. The Compensation Committee
and the Board of Directors believe that EBITDA as adjusted per share is a useful
indicator of funds available to the Company which may be used to make
investments in new affiliates, repay indebtedness, repurchase shares of Common
Stock or pay dividends on Common Stock.
 
    As set forth above under "--Option Grants in 1998," the Compensation
Committee granted stock options to Mr. Nutt and the other executive officers of
the Company in 1998. The Compensation Committee based the size of the option
grants on the same factors considered in making performance-based compensation
decisions, as described above.
 
WILLIAM J. NUTT
P. ANDREWS MCLANE
JOHN M. B. O'CONNOR
 
                                       10

                       COMPENSATION COMMITTEE INTERLOCKS
                           AND INSIDER PARTICIPATION
 
    The Company's executive compensation is determined by the Compensation
Committee of the Board of Directors, which currently consists of Messrs. Nutt,
McLane and O'Connor. Mr. Nutt serves as Chairman, President and Chief Executive
Officer of the Company. Mr. Nutt does not participate in the consideration or
recommendation of his own compensation arrangements.
 
                              CERTAIN TRANSACTIONS
 
    In December 1998, the Company made loans to Sean M. Healey, Executive Vice
President of the Company, in the amount of $800,000 and Darrell W. Crate, Senior
Vice President and Chief Financial Officer of the Company, in the amount of
$900,000. Each loan has a 30 year maturity (but accelerates upon termination of
employment) and is secured by real property. The rate of interest charged on
each loan is the lesser of 6.25% or the Company's cost of borrowing.
 
    In August 1995, the Skyline Funds, for which Skyline Asset Management, L.P.
(one of the investment management firms ("Affiliates") in which the Company
holds a majority interest) provides investment advisory services, retained Funds
Distributor, Inc. as a distributor of shares in the Skyline Funds. Mr. Nutt is
Chairman of Funds Distributor, Inc., and the Chairman and Chief Executive
Officer and majority stockholder of its parent, Boston Institutional Group, Inc.
During 1998, the Skyline Funds paid Funds Distributor, Inc. approximately
$143,388.
 
    During 1998, the Company retained Goodwin, Procter & Hoar LLP for certain
legal services. Richard E. Floor, a director of the Company, is the sole
shareholder of Richard E. Floor, P.C., which is a partner in Goodwin, Procter &
Hoar LLP.
 
    During 1998, in connection with the Company's senior credit facility (the
"Credit Facility") with a syndicate of banks managed by The Chase Manhattan
Bank, as Administrative Agent, and Nationsbank, N.A., as Documentation Agent,
the Company paid The Chase Manhattan Bank an administrative agency fee of
$75,000. In addition, the Company paid each of The Chase Manhattan Bank and
Nationsbank, N.A. interest under the Credit Facility in accordance with its
terms.
 
    Chase Equity Associates, L.P. (a stockholder of the Company) is a limited
partnership whose sole limited partner is an affiliate of Chase Manhattan
Corporation (the parent company of The Chase Manhattan Bank) and whose sole
general partner has as its partners certain employees of The Chase Manhattan
Bank (including John M.B. O'Connor, a director of the Company) and an affiliate
of Chase Manhattan Corporation. W.W. Walker, Jr., a director of the Company, is
Senior Managing Director of Bank of America Capital Investors, an affiliate of
Nationsbank, N.A.
 
             PROPOSAL 2: APPROVAL OF THE AMENDMENT AND RESTATEMENT
             OF THE COMPANY'S 1997 STOCK OPTION AND INCENTIVE PLAN
 
INTRODUCTION
 
    On April 14, 1999, the Board of Directors adopted, subject to stockholder
approval at the Annual Meeting, the Plan Amendment pursuant to which the
following changes would be made to the 1997 Stock Plan:
 
    - The number of shares of Common Stock reserved for issuance under the 1997
      Stock Plan would be increased from 1,750,000 to 3,250,000.
 
    - The 1997 Stock Plan is administered by the Board of Directors or the
      Compensation Committee (the "Administrator"). The Administrator of the
      1997 Stock Plan would be prohibited from reducing the exercise price of
      any outstanding stock option or stock appreciation right without the
 
                                       11

      approval of the Company's stockholders entitled to vote on such matter at
      a meeting of stockholders.
 
    - No stock options would be exercisable more than ten years after the date
      of grant. The 1997 Stock Plan currently provides that Non-Qualified Stock
      Options (as defined below) may be granted with terms that exceed ten
      years.
 
    - Optionees would be permitted, at the discretion of the Administrator of
      the 1997 Stock Plan, to exercise stock options by attesting to the
      ownership of shares of unrestricted Common Stock with a fair market value
      equal to the exercise price of the options. Upon such an exercise, the
      optionee would be issued a number of shares of Common Stock net of the
      number of shares attested to.
 
    - The Board of Directors would be authorized, in its discretion, to grant
      loans to selected key employees to be used solely for the purchase of
      shares of Common Stock or the payment of taxes in connection with awards
      under the 1997 Stock Plan. These loans could be made with or without
      recourse against the employee, but would be secured by the shares of
      Common Stock in respect of which the loans were granted.
 
    - To ensure that certain awards granted under the 1997 Stock Plan to the
      Company's Chief Executive Officer and the four other most
      highly-compensated executive officers during any fiscal year qualify as
      "performance-based compensation" under Section 162(m) of the Internal
      Revenue Code of 1986, as amended (the "Code"), the Administrator of the
      1997 Stock Plan would be permitted to require that the vesting of such
      awards be conditioned on the satisfaction of performance criteria which
      may include any or all of the following: (i) EBITDA; (ii) EBITDA as
      adjusted per share; (iii) return on equity, assets, capital or investment;
      (iv) pre-tax or after-tax profit levels of the Company or any subsidiary,
      division, operating unit or business segment thereof, or any combination
      of the foregoing; (v) assets under management; (vi) total shareholder
      return; (vii) changes in the market price of the Common Stock; or (viii)
      earnings per share. The Administrator of the 1997 Stock Plan will select
      the particular performance criteria within 90 days following the
      commencement of a performance cycle.
 
REASONS FOR THE PLAN AMENDMENT
 
    The Board of Directors believes that the Company's growth and long-term
success depend in large part upon retaining and motivating key personnel and
that such retention and motivation can be achieved in part through grants under
the 1997 Stock Plan. The Board of Directors also believes that stock options and
other equity-based awards can play an important role in the success of the
Company by encouraging and enabling the officers and other employees of the
Company, upon whose judgment, initiative and efforts the Company depends for
sustained growth and profitability, to acquire a proprietary interest in the
long-term performance of the Company. The Board of Directors anticipates that
providing such persons with a direct stake in the Company will ensure a closer
identification of the interests of the participants in the 1997 Stock Plan with
those of the Company, thereby stimulating the efforts of such participants to
promote the Company's future success and strengthen their desire to remain with
the Company.
 
    The Board of Directors believes that increasing the number of shares
issuable under the 1997 Stock Plan and authorizing the grant of loans to key
employees in connection with awards under the 1997 Stock Plan will help the
Company accomplish these goals and will keep the Company's equity incentive
compensation in line with that of its competitors. In addition, the Board of
Directors believes that permitting an optionee to exercise options by attesting
to the ownership of unrestricted Common Stock with a fair market value equal to
the exercise price of the options will eliminate administrative burdens for
employees without changing the benefits to the Company upon such an exercise.
 
                                       12

    The Board of Directors also believes that it is important to the Company's
stockholders that employees who receive awards under the 1997 Stock Plan benefit
from increases in the market price of the Common Stock, and suffer from
decreases in the market price of the Common Stock, together with the Company's
stockholders. The Board believes that prohibiting the repricing of stock options
and stock appreciation rights will further the alignment of the interests of
grantees under the 1997 Stock Plan with those of the Company's stockholders. The
Board of Directors also believes that limiting the maximum length of
exercisability of stock options to ten years will also align the interests of
grantees under the 1997 Stock Plan with those of the Company's stockholders.
 
    Finally, Section 162(m) of the Code and the regulations thereunder generally
would disallow a federal income tax deduction to the Company for compensation in
excess of $1 million paid in any year to any of those Executive Officers
included in the Summary Compensation Table for any fiscal year who are employed
by the Company on the last day of the such year ("Covered Employees"). However,
this limitation on compensation expense does not apply to payments of
"performance-based compensation," the material terms of which have been approved
by stockholders. Certain awards under the 1997 Stock Plan to Covered Employees
are intended to be "performance-based compensation" for this purpose, and the
1997 Stock Plan would be revised by the Plan Amendment accordingly.
 
RECOMMENDATION
 
    THE BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS A VOTE FOR APPROVAL OF THE
AMENDMENT AND RESTATEMENT OF THE 1997 STOCK PLAN.
 
SUMMARY OF THE 1997 STOCK PLAN
 
    The following description of certain features of the 1997 Stock Plan is
intended to be a summary only and does not describe every provision of the 1997
Stock Plan.
 
    INTRODUCTION.  The 1997 Stock Plan was adopted by the Board of Directors in
October 1997 and was subsequently approved by the Company's stockholders. The
1997 Stock Plan permits (i) the grant of options to purchase shares of Common
Stock intended to qualify as incentive stock options under the Code ("Incentive
Options"), (ii) the grant of options that do not so qualify ("Non-Qualified
Options"), (iii) the grant of stock appreciation rights, (iv) the issuance or
sale of Common Stock with vesting or other restrictions ("Restricted Stock"),
(v) the issuance or sale of Common Stock without restrictions ("Unrestricted
Stock"), (vi) the grant of the right to receive Common Stock in the future with
or without vesting or other restrictions ("Deferred Stock Awards"), (vii) the
grant of Common Stock upon the attainment of specified performance goals
("Performance Share Awards"), and (viii) the grant of the right to receive cash
dividends with the holders of the Common Stock as if the recipient held a
specified number of shares of the Common Stock ("Dividend Equivalent Rights").
These grants may be made to officers and other employees, directors, advisors,
consultants and other key persons of the Company and its subsidiaries. The 1997
Stock Plan currently provides for the issuance of 1,750,000 shares of Common
Stock. If adopted, the Plan Amendment would increase the number of shares of
Common Stock authorized and reserved for issuance to 3,250,000. Options or stock
appreciation rights with respect to no more than 700,000 shares of Common Stock
may be granted to any one individual in any calendar year.
 
    PLAN ADMINISTRATION; ELIGIBILITY.  If the 1997 Stock Plan is administered by
the Compensation Committee, then all members of the Compensation Committee must
be "disinterested persons" as that term is defined under the rules promulgated
by the Commission, and "outside directors" as defined in Section 162(m) of the
Code and the regulations promulgated thereunder. The Administrator has full
power to select, from among the employees and other persons eligible for awards,
the individuals to whom awards will be granted, to make any combination of
awards to participants, and to determine the specific terms and conditions of
each award, subject to the provisions of the 1997 Stock Plan.
 
                                       13

    Persons eligible to participate in the 1997 Stock Plan are those officers,
employees and other key persons, such as consultants, of the Company and its
subsidiaries who are responsible for or contribute to the management, growth or
profitability of the Company and its subsidiaries, as selected from time to time
by the Administrator. Non-employee Directors are also eligible for certain
awards under the 1997 Stock Plan.
 
    STOCK OPTIONS.  The 1997 Stock Plan permits the granting of (i) Incentive
Options and (ii) Non-Qualified Options. Only employees of the Company and its
subsidiaries may be granted Incentive Options. The option exercise price of each
option will be determined by the Administrator but may not be less than 100% of
the fair market value of the Common Stock on the date of grant in the case of
Incentive Options, and may not be less than 85% of the fair market value of the
Common Stock on the date of grant in the case of Non-Qualified Options.
Employees participating in the 1997 Stock Plan may, however, elect, with the
consent of the Administrator, to receive discounted Non-Qualified Options in
lieu of cash bonuses. In the case of such grants, the option exercise price may
be less than 85% of the fair market value of the Common Stock on the date of
grant.
 
    STOCK OPTIONS GRANTED TO NON-EMPLOYEE DIRECTORS.  The 1997 Stock Plan
contemplates the grant to each additional non-employee Director of a
Non-Qualified Option upon his or her initial election to the Board of Directors.
The exercise price of each such Non-Qualified Option is the fair market value of
the Common Stock on the date of grant, and each such grant is subject to vesting
requirements as determined by the Administrator. The Administrator may also
grant additional Non-Qualified Options to non-employee Directors.
 
    STOCK APPRECIATION RIGHTS.  The Administrator may award a stock appreciation
right ("SAR") either as a freestanding award or in tandem with a stock option.
Upon exercise of the SAR, the holder will be entitled to receive an amount equal
to the excess of the fair market value on the date of exercise of one share of
Common Stock over the exercise price per share specified in the related stock
option (or, in the case of a freestanding SAR, the price per share specified in
such right, which price may not be less than 85% of the fair market value of the
Common Stock on the date of grant) times the number of shares of Common Stock
with respect to which the SAR is exercised. This amount may be paid in cash,
Common Stock, or a combination thereof, as determined by the Administrator.
 
    RESTRICTED STOCK.  The Administrator may also award shares of Restricted
Stock to officers, other employees and key persons of the Company. The
conditions and restrictions applicable to the Restricted Stock may include the
achievement of certain performance goals and/or continued employment with the
Company through a specified restricted period. These conditions and
restrictions, as well as the purchase price of shares of Restricted Stock, are
determined by the Administrator. If the performance goals and other restrictions
are not attained, the employees forfeit their awards of Restricted Stock.
 
    UNRESTRICTED STOCK.  The Administrator may also grant shares (at no cost or
for a purchase price determined by the Administrator) of Unrestricted Stock to
employees and key persons in recognition of past services or other valid
consideration, and shares of Unrestricted Stock may be issued in lieu of cash
compensation to be paid to such employees and key persons.
 
    DEFERRED STOCK AWARDS.  The Administrator may also award Deferred Stock
Awards which are ultimately payable in the form of shares of Unrestricted Stock.
The Deferred Stock Awards may be subject to such conditions and restrictions as
the Administrator may determine, including the achievement of certain
performance goals and/or continued employment with the Company through a
specified restricted period. If the performance goals and other restrictions are
not attained, the participants forfeit their Deferred Stock Awards.
 
                                       14

    Subject to the consent of the Administrator, a non-employee Director, an
employee or key person of the Company may make an irrevocable election to
receive a portion of his fees or compensation in Deferred Stock Awards (valued
at fair market value on the date the cash compensation would otherwise be paid).
 
    PERFORMANCE SHARE AWARDS.  The Administrator may also grant Performance
Share Awards to employees or other key persons of the Company entitling the
recipient to receive shares of Common Stock upon the achievement of individual
or Company performance goals and such other conditions as the Administrator
shall determine.
 
    DIVIDEND EQUIVALENT RIGHTS.  The Administrator may grant Dividend Equivalent
Rights, which give the recipient the right to receive credits for dividends that
would be paid if the grantee had held a specified number of shares of Common
Stock. Dividend Equivalent Rights may be settled in cash, shares, or a
combination thereof.
 
    AMENDMENTS AND TERMINATION.  The Board of Directors may at any time amend or
discontinue the 1997 Stock Plan and the Administrator may at any time amend or
cancel outstanding awards for the purpose of satisfying changes in the law or
for any other lawful purpose. No such action may be taken, however, which
adversely affects any rights under outstanding awards without the holder's
consent. Further, amendments to the 1997 Stock Plan shall be subject to approval
by the Company's stockholders if and to the extent required by the Code to
preserve the qualified status of Incentive Options or to preserve tax
deductibility of compensation earned under stock options and stock appreciation
rights.
 
    CHANGE IN CONTROL PROVISIONS.  The 1997 Stock Plan provides that in the
event of a sale of all or substantially all of the assets or Common Stock of the
Company, a merger or consolidation which results in a change in control of the
Company or the liquidation or dissolution of the Company (a "Change in
Control"), all stock options and stock appreciation rights shall automatically
become fully exercisable. In addition, at any time prior to or after a Change of
Control, the Administrator may accelerate awards and waive conditions and
restrictions on any awards to the extent it may determine appropriate.
 
    NEW 1997 STOCK PLAN BENEFITS.  No grants have been made with respect to the
additional shares of Common Stock which would be reserved for issuance if the
Plan Amendment is approved by stockholders. The number of shares of Common Stock
that may be granted to executive officers and non-executive officers is
indeterminable at this time.
 
TAX ASPECTS UNDER THE U.S. INTERNAL REVENUE CODE
 
    The following is a summary of the principal federal income tax consequences
of transactions under the 1997 Stock Plan. It does not describe all federal tax
consequences under the 1997 Stock Plan, nor does it describe state or local tax
consequences.
 
    INCENTIVE OPTIONS.  No taxable income is generally realized by the optionee
upon the grant or exercise of an Incentive Option. If shares of Common Stock
issued to an optionee pursuant to the exercise of an Incentive Option are sold
or transferred after two years from the date of grant and after one year from
the date of exercise, then (i) upon sale of such shares, any amount realized in
excess of the option price (the amount paid for the shares) will be taxed to the
optionee as a long-term capital gain, and any loss sustained will be a long-term
capital loss, and (ii) there will be no deduction for the Company for federal
income tax purposes. The exercise of an Incentive Option will give rise to an
item of tax preference that may result in alternative minimum tax liability for
the optionee.
 
                                       15

    If shares of Common Stock acquired upon the exercise of an Incentive Option
are disposed of prior to the expiration of the two-year and one-year holding
periods described above (a "disqualifying disposition"), generally (i) the
optionee will realize ordinary income in the year of disposition in an amount
equal to the excess (if any) of the fair market value of the shares of common
stock at exercise (or, if less, the amount realized on a sale of such shares of
common stock) over the option price thereof, and (ii) the Company will be
entitled to deduct such amount. Special rules will apply where all or a portion
of the exercise price of the Incentive Option is paid by tendering shares of
Common Stock.
 
    If an Incentive Option is exercised at a time when it no longer qualifies
for the tax treatment described above, the option is treated as a Non-Qualified
Option. Generally, an Incentive Option will not be eligible for the tax
treatment described above if it is exercised more than three months following
termination of employment (or one year in the case of termination of employment
by reason of disability). In the case of termination of employment by reason of
death, the three-month rule does not apply.
 
    NON-QUALIFIED OPTIONS.  With respect to Non-Qualified Options under the 1997
Stock Plan, no income is realized by the optionee at the time the option is
granted. Generally (i) at exercise, ordinary income is realized by the optionee
in an amount equal to the difference between the option price and the fair
market value of the shares of Common Stock on the date of exercise, and the
Company receives a tax deduction for the same amount, and (ii) at disposition,
appreciation or depreciation after the date of exercise is treated as either
short-term or long-term capital gain or loss depending on how long the shares of
Common Stock have been held. Special rules will apply where all or a portion of
the exercise price of the Non-Qualified Option is paid by tendering shares of
Common Stock.
 
    PARACHUTE PAYMENTS.  The vesting of any portion of any option or other award
that is accelerated due to the occurrence of a Change of Control may cause a
portion of the payments with respect to such accelerated awards to be treated as
"parachute payments" as defined in the Code. Any such parachute payments may be
non-deductible to the Company, in whole or in part, and may subject the
recipient to a non-deductible 20% federal excise tax on all or a portion of such
payment (in addition to other taxes ordinarily payable).
 
    LIMITATION ON COMPANY'S DEDUCTIONS.  As a result of Section 162(m) of the
Code, the Company's deduction for certain awards under the 1997 Stock Plan may
be limited to the extent that a Covered Employee receives compensation in excess
of $1 million in such taxable year of the Company (other than performance-based
compensation that otherwise meets the requirements of Section 162(m) of the
Code).
 
                                       16

                      SECURITY OWNERSHIP OF MANAGEMENT AND
                           CERTAIN BENEFICIAL OWNERS
 
    The following table sets forth as of March 26, 1999 certain information
regarding the beneficial ownership of Common Stock by (i) each person or "group"
(as that term is defined in Section 13(d)(3) of the Exchange Act) known by the
Company to be the beneficial owner of more than 5% of the Common Stock, (ii)
each executive officer of the Company, (iii) each director and Nominee and (iv)
all directors and executive officers as a group (13 persons). Except as
otherwise indicated, the Company believes, based on information furnished by
such persons, that each person listed below has sole voting and investment power
over the shares of Common Stock shown as beneficially owned, subject to
community property laws, where applicable.
 


                                                        NUMBER OF SHARES
                                                          BENEFICIALLY        PERCENT OF
NAME OF BENEFICIAL OWNER(1)                                   OWNED         COMMON STOCK(2)
- - ------------------------------------------------------  -----------------  -----------------
                                                                     
Chase Equity Associates, L.P..........................        1,271,929(3)           5.5%
BankAmerica Corporation...............................        1,105,160(4)           4.7%
William J. Nutt.......................................          552,824(5)           2.4%
Sean M. Healey........................................          217,514(6)           1.0%
Levon Chertavian, Jr..................................           95,056(7)             *
Nathaniel Dalton......................................           59,958(8)             *
Darrell W. Crate......................................           51,000(9)             *
Seth W. Brennan.......................................           31,569(10)             *
Jeffrey S. Murphy.....................................           16,778(11)             *
Daniel J. Shea........................................            6,250(12)             *
Richard E. Floor......................................           41,492                *
P. Andrews McLane.....................................           40,581(13)             *
W. W. Walker, Jr......................................               --               --
John M. B. O'Connor...................................        1,271,929(14)           5.5%
William F. Weld.......................................            3,125(15)             *
All directors and executive officers as a group (13
  persons)............................................        2,388,076(16)          10.3%

 
- - ------------------------
 
*   Less than 1%
 
(1) Unless otherwise indicated, the mailing address for each stockholder and
    director is c/o AMG, Two International Place, 23rd Floor, Boston,
    Massachusetts, 02110. The address of Chase Equity Associates, L.P. is 380
    Madison Avenue, 12th Floor, New York, New York 10017. The address of
    BankAmerica Corporation is c/o Bank of America Capital Investors, Bank of
    America Corporate Center, 25th Floor, 100 North Tryon Street, Charlotte,
    North Carolina 28255.
 
(2) In computing the number of shares of Common Stock beneficially owned by a
    person, shares of Common Stock subject to options and warrants held by that
    person that are currently exercisable or that become exercisable within 60
    days of March 26, 1999 are deemed outstanding. For purposes of computing the
    percentage of outstanding shares of Common Stock beneficially owned by such
    person, such shares of stock subject to options or warrants that are
    currently exercisable or that become exercisable within 60 days of March 26,
    1999 are deemed to be outstanding for such person but are not deemed to be
    outstanding for purposes of computing the ownership percentage of any other
    person. As of March 26, 1999, a total of 23,547,948 shares of Common Stock
    were either outstanding or subject to options, warrants or other convertible
    securities that are exercisable or that will become exercisable within 60
    days.
 
(3) The 1,271,929 shares beneficially owned by Chase Equity Associates, L.P. are
    shares of non-voting Class B Common Stock, convertible under certain
    circumstances into voting Common Stock.
 
                                       17

(4) The 1,105,160 shares beneficially owned by BankAmerica Corporation include
    (i) 550,000 shares of Common Stock and 220,150 shares of non-voting Class B
    Common Stock beneficially owned by NationsBanc Investment Corporation; (ii)
    235,800 shares beneficially owned by NationsBank, N.A., of which 206,400
    shares are held by TradeStreet Investment Associates, Inc., of which 122,700
    shares are under the discretionary authority of NationsBank Advisors, Inc.;
    (iii) 90,400 shares beneficially owned by Bank of America National Trust and
    Savings Association; and (iv) 8,810 shares held by BankAmerica Capital
    Corporation. BankAmerica Corporation is a bank holding company and the
    direct or indirect parent of NationsBanc Investment Corporation, Bank of
    America National Trust and Savings Association, BankAmerica Capital
    Corporation and NB Holdings Corporation, NB Holdings Corporation is a
    holding company and the direct parent of NationsBanc Investment Corporation
    and NationsBank, N.A. NationsBank, N.A. is a national bank and the direct
    parent of Trade Street Investment Associates, Inc. and NationsBanc Advisors,
    Inc.
 
(5) Includes 60,264 shares of Common Stock subject to options exercisable within
    60 days. Excludes (i) 227,236 shares subject to unvested options and (ii)
    89,139 shares held by irrevocable trusts for the benefit of members of Mr.
    Nutt's immediate family of which Mr. Nutt is not a trustee, of which shares
    Mr. Nutt disclaims beneficial ownership.
 
(6) Includes 57,514 shares of Common Stock subject to options exercisable within
    60 days. Excludes 212,486 shares subject to unvested options.
 
(7) Includes 20,056 shares of Common Stock subject to options exercisable within
    60 days. Excludes 62,444 shares subject to unvested options.
 
(8) Includes 31,958 shares of Common Stock subject to options exercisable within
    60 days. Excludes 106,042 shares subject to unvested options.
 
(9) Represents 50,000 shares of Common Stock subject to options exercisable with
    60 days. Excludes 90,000 shares subject to unvested options.
 
(10) Includes 25,069 shares of Common Stock subject to options exercisable
    within 60 days. Excludes 79,931 shares subject to unvested options.
 
(11) Includes 14,278 shares of Common Stock subject to options exercisable
    within 60 days. Excludes 53,722 shares subject to unvested options.
 
(12) Represents 6,250 shares of Common Stock subject to options exercisable with
    60 days. Excludes 40,750 shares subject to unvested options.
 
(13) Includes 27,129 shares owned by Arboretum LP, of which Mr. McLane serves as
    a managing member of the general partner. Excludes 24,226 shares held by
    irrevocable trusts for the benefit of members of Mr. McLane's immediate
    family of which Mr. McLane is not a trustee, of which shares Mr. McLane
    disclaims beneficial ownership.
 
(14) Represents 1,271,929 shares of non-voting Class B Common Stock beneficially
    owned by Chase Equity Associates, L.P., of which shares of Mr. O'Connor
    disclaims beneficial ownership.
 
(15) Represents 3,125 shares of Common Stock subject to options exercisable
    within 60 days. Excludes 8,625 shares subjected to unvested options.
 
(16) Includes 2,388,076 shares of Common Stock held by executive officers and
    directors which are subject to vesting and repurchase in certain
    circumstances.
 
                                       18

                                 OTHER MATTERS
 
SECTION 16(A) BENEFICIAL OWNERSHIP REPORTING COMPLIANCE
 
    Section 16(a) of the Exchange Act requires the Company's executive officers,
directors and persons who own more than 10% of a registered class of the
Company's equity securities, to file reports of ownership and changes in
ownership with the SEC and the New York Stock Exchange. Officers, directors and
greater than 10% stockholders are required by SEC regulations to furnish the
Company copies of all Section 16(a) forms they file. To the Company's knowledge,
based solely on a review of the copies of such reports provided to the Company
and written representations from certain reporting persons that no other reports
were required during, or with respect to, 1998, all Section 16(a) filing
requirements applicable to its executive officers, directors and greater than
10% beneficial owners have been satisfied, except for Daniel J. Shea who
inadvertently failed to file a Form 3 with the SEC on a timely basis following
the commencement of his employment with the Company.
 
INDEPENDENT PUBLIC ACCOUNTANTS
 
    The accounting firm of PricewaterhouseCoopers LLP served as the Company's
independent public accountants during 1998 and is expected to continue to do so
for fiscal year 1999. A representative of PricewaterhouseCoopers LLP is expected
to be present at the Annual Meeting, will be given an opportunity to make a
statement if he or she so desires and will be available to respond to
appropriate questions.
 
EXPENSES OF SOLICITATION
 
    The cost of solicitation of proxies will be borne by the Company. In an
effort to have as large a representation at the Annual Meeting as possible,
special solicitation of proxies may, in certain instances, be made personally or
by telephone, telegraph or mail by one or more employees of the Company. The
Company also may reimburse brokers, banks, nominees and other fiduciaries for
postage and reasonable clerical expenses of forwarding the proxy materials to
their principals who are beneficial owners of Common Stock.
 
STOCKHOLDER PROPOSALS
 
    Any stockholder proposals submitted pursuant to Exchange Act Rule 14a-8 and
intended to be presented at the Company's 2000 Annual Meeting of Stockholders
must be received by the Company at its principal executive office on or before
December 24, 1999 to be eligible for inclusion in the proxy statement and form
of proxy to be distributed by the Board of Directors in connection with such
meeting.
 
    Any stockholder proposals (including recommendations of nominees for
election to the Board of Directors) intended to be presented at the Company's
2000 Annual Meeting of Stockholders, other than a stockholder proposal submitted
pursuant to Exchange Act Rule 14a-8, must be received in writing at the
principal executive office of the Company no later than March 11, 2000, nor
prior to January 26, 2000, together with all supporting documentation required
by the By-laws. Proxies solicited by the Board of Directors will confer
discretionary voting authority with respect to these proposals, subject to SEC
rules governing the exercise of this authority.
 
OTHER MATTERS
 
    The Board of Directors does not know of any matters other than those
described in this Proxy Statement which will be presented for action at the
Annual Meeting. If other matters are presented, proxies will be voted in
accordance with the best judgment of the proxy holders.
 
                                       19

A COPY OF THE COMPANY'S ANNUAL REPORT ON FORM 10-K FOR 1998 (INCLUDING FINANCIAL
STATEMENTS AND SCHEDULES THERETO), WHICH WAS FILED WITH THE SECURITIES AND
EXCHANGE COMMISSION ON MARCH 31, 1999, WILL BE PROVIDED WITHOUT CHARGE TO ANY
PERSON TO WHOM THIS PROXY STATEMENT IS MAILED UPON THE WRITTEN REQUEST OF ANY
SUCH PERSON TO NATHANIEL DALTON, SENIOR VICE PRESIDENT, GENERAL COUNSEL AND
SECRETARY, AFFILIATED MANAGERS GROUP, INC., TWO INTERNATIONAL PLACE, 23RD FLOOR,
BOSTON, MASSACHUSETTS 02110.
 
REGARDLESS OF THE NUMBER OF SHARES YOU OWN, YOUR VOTE IS IMPORTANT TO THE
COMPANY. PLEASE COMPLETE, SIGN, DATE AND PROMPTLY RETURN THE ENCLOSED PROXY CARD
TODAY.
 
                                       20


                                     PROXY

       TWO INTERNATIONAL PLACE, 23RD FLOOR, BOSTON, MASSACHUSETTS 02110

                            PROXY FOR COMMON STOCK

          THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS

    The undersigned hereby appoints William J. Nutt, Sean M. Healey and 
Nathaniel Dalton, and each of them, proxies with full power of substitution 
to vote for and on behalf on the undersigned at the Annual Meeting of 
Stockholders of Affiliated Managers Group, Inc. (the "Company"), to be held at 
the offices of Goodwin, Procter & Hoar LLP at Exchange Place, 53 State 
Street, Boston, Massachusetts 02109 on Tuesday, May 25, 1999 at 9:00 a.m., 
Boston time, and at any adjournments or postponements thereof, hereby 
granting full power and authority to act on behalf of the undersigned at said 
meeting and any adjournments or postponements thereof. The undersigned hereby 
revokes any proxy previously given in connection with such meeting and 
acknowledges receipt of the Notice of Annual Meeting of Stockholders and 
Proxy Statement and the 1998 Annual Report to Stockholders.

     THIS PROXY, WHEN PROPERLY EXECUTED, WILL BE VOTED IN THE MANNER DIRECTED 
HEREIN BY THE UNDERSIGNED STOCKHOLDER. IF NO INSTRUCTION IS INDICATED, THE 
UNDERSIGNED'S VOTE WILL BE CAST "FOR" EACH OF THE NOMINEES FOR DIRECTOR OF 
THE COMPANY NAMED IN THE ACCOMPANYING PROXY STATEMENT. The undersigned's 
votes will be cast in accordance with the proxies' discretion on such other 
business as may properly come before the meeting or any adjournments or 
postponements thereof. PLEASE SIGN AND RETURN PROMPTLY IN THE ENCLOSED 
ENVELOPE.

              CONTINUED, AND TO BE SIGNED, ON REVERSE SIDE

                        FOLD AND DETACH HERE



1. Proposal to elect William J. Nutt, P. Andrews McLane, Richard E. Floor, 
W.W. Walker, Jr., John M.B. O'Connor and William F. Weld as directors of the 
Company, each for a one-year-term to continue until the 2000 Annual Meeting 
of Stockholders and until the successor of each is duly elected and qualified.

                    FOR                 WITHHELD
                    ALL                 FOR ALL
                    / /                   / /


_____________________________________________________
Withheld as to the nominees noted above


2. Proposal to approve the amendment and restatement of the Affiliated 
Managers Group, Inc. 1997 Stock Option and Incentive Plan.

                  FOR              AGAINST          ABSTAIN
                  / /                / /              / /


3. To consider and act upon such other business as may properly come before 
the meeting or any adjournments or postponements thereof.


                                       Date _____________________________, 1999


                                       Signature: _____________________________


                                       Signature: _____________________________

                                       For joint accounts, each owner should 
                                       sign. Executors, administrators,
                                       trustees, corporate officers and others
                                       acting in a representative capacity
                                       should give full title or authority.


                             FOLD AND DETACH HERE