Exhibit 10.51a

                    REGISTRATION RIGHTS AND LOCK-UP AGREEMENT

        THIS REGISTRATION RIGHTS AND LOCK-UP AGREEMENT (this "Agreement"), is
made and entered into as of February 15, 2005, by and among Acadia Realty Trust,
a Maryland real estate investment trust (the "REIT"), Acadia Realty Limited
Partnership, a Delaware limited partnership (the "Partnership"), and the
undersigned Klaff Realty, LP, a Delaware limited Partnership ("Klaff"), which,
as of February 15, 2005 (the "Closing Date") of the transactions contemplated by
the Agreement of Contribution by and among Klaff and Klaff Realty, Limited, the
REIT, and the Partnership (the "Contribution Agreement"), are receiving common
units of limited partnership interests in the Partnership ("Units"), which are
exchangeable for Conversion Shares (as defined below).

        NOW, THEREFORE, in consideration of the premises and the mutual
covenants contained herein, and intending to be legally bound hereby, the REIT,
the Partnership and Klaff hereby agree as follows:

        1.      Certain Definitions. As used in this Agreement, the following
terms shall have the following respective meanings:

                (a)     "Commission" means the Securities and Exchange
Commission, or any other federal agency at the time administering the Securities
Act.

                (b)     "Conversion Shares" means the Shares issuable upon
exchange of the Units from time to time.

                (c)     "Exchange Act" means the Securities Exchange Act of
1934, as amended, or any successor federal statute, and the rules and
regulations of the Commission issued under such Exchange Act, as they each may,
from time to time, be in effect.

                (d)     "Holder(s)" means a holder of Registrable Shares
entitled to the rights arising hereunder.

                (e)     "Participating Holder" means a Holder whose Registrable
Shares are included in a Registration Statement.

                (f)     "Registration Expenses" means the expenses described in
Section 4 hereof.

                (g)     "Registration Statement" means a registration statement
filed by the REIT with the Commission for a public offering and sale of equity
securities of the REIT (other than a registration statement on Form S-8 or Form
S-4, or their successors, or any registration statement covering only securities
proposed to be issued in exchange for securities or assets of another
corporation).

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                (h)     "Registrable Shares" means (i) the Conversion Shares,
(ii) any other Shares issued in respect of Conversion Shares, and (iii) any
other Shares issued with respect to the Shares issued in clauses (i) and (ii)
(because of share splits, share dividends, reclassifications, recapitalizations,
or similar events); provided, however, that Shares which are Registrable Shares
shall cease to be Registrable Shares (x) upon any sale pursuant to a
Registration Statement, or any other sale or transfer of the Registrable Shares
in any manner to any person or entity other than a Permitted Transferee (as
defined) or as otherwise expressly provided herein, or (y) in the event that
Registrable Shares may be freely sold and/or transferred pursuant to Rule 144(k)
under the Securities Act.

                (i)     "Securities Act" means the Securities Act of 1933, as
amended, or any successor federal statute, and the rules and regulations of the
Commission issued under such Securities Act, as they each may, from time to
time, be in effect.

                (j)     "Shares" means Common Shares of Beneficial Interest of
the REIT, par value $.001 per share.

        2.      Certain Shelf Registration. Within one hundred fifty (150) days
from the date of this Agreement, the REIT shall, at its expense, file a shelf
Registration Statement pursuant to Rule 415 under the Securities Act to register
the Registrable Shares for resale, including for issuance upon conversion or
exchange of Units. The REIT shall, at its expense, use commercially reasonable
efforts to maintain the effectiveness of such shelf Registration Statement until
the earlier of (i) such time as when all of the Registrable Shares have been
disposed of or (ii) three years after the conversion or exchange into Shares of
all of the Units.

        3.      Registration Procedures. If and whenever the REIT is required by
the provisions of this Agreement to effect the registration of any of the
Registrable Shares under the Securities Act, the REIT shall, at its expense:

                (a)     prepare and file with the Commission a Registration
Statement with respect to such Registrable Shares and use best efforts to cause
that Registration Statement to become effective;

                (b)     use commercially reasonable efforts to cause the
Registration Statement to remain effective;

                (c)     subject to the provision of Section 2, promptly prepare
and file with the Commission any amendments and supplements to the Registration
Statement and the prospectus included in the Registration Statement as may be
necessary to keep the Registration Statement effective for the period of time
required by the Commission;

                (d)     promptly furnish to each Participating Holder such
reasonable numbers of copies of the prospectus, including a preliminary
prospectus, in conformity with the requirements of the Securities Act, and such
other documents as the Participating Holders may reasonably request in order to
facilitate the public sale or other disposition of the Registrable Shares owned
by such Participating Holders and included in the Registration Statement; and

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                (e)     promptly use commercially reasonable efforts to register
or qualify the Registrable Shares covered by the Registration Statement under
the securities or Blue Sky laws of states within the United States as the
Participating Holders shall reasonably request; provided, however, that the REIT
shall not be required in connection with this subsection 3(e) to: (i) qualify as
a foreign corporation in any jurisdiction where, but for the requirements of
this subsection 3(e), it would not be obligated to be so qualified; (ii) execute
a general consent to service of process in any jurisdiction; (iii) subject
itself to taxation in any such jurisdiction; or (iv) register in any state
requiring, as a condition to registration, escrow or surrender of any REIT
securities held by any security holder other than the Participating Holders.

        If the REIT has delivered a preliminary or final prospectus to a
Participating Holder and, after having done so, the prospectus is amended to
comply with the requirements of the Securities Act, the REIT shall promptly
notify such Participating Holder and, if requested, such Participating Holder
shall immediately cease making offers of Registrable Shares and return all
prospectuses to the REIT. The REIT shall promptly provide Participating Holders
with revised prospectuses and, following receipt of the revised prospectuses,
Participating Holders shall be free to resume making offers of the Registrable
Shares.

        Notwithstanding any other provisions of this Agreement to the contrary,
upon receipt by a Participating Holder of a written notice signed by the Chief
Executive Officer, General Counsel or Chief Financial Officer of the REIT, to
the effect set forth below, the REIT shall not be obligated during a reasonable
period of time thereafter to effect any registrations pursuant to this
Agreement, and each such Participating Holder agrees that it will immediately
suspend sales of Shares under any effective Registration Statement for a
reasonable period of time, in either case not to exceed 90 days, at any time
during which, in the REIT's reasonable judgment, (i) there is a development
involving the REIT or any of its affiliates which is material but which has not
yet been publicly disclosed or (ii) sales pursuant to the Registration Statement
would materially and adversely affect an underwritten public offering for the
account of the REIT or any other material financing project or where a proposed
or pending material merger or other material acquisition or material business
combination or material disposition of the REIT's assets, to which the REIT or
any of its affiliates is, or is expected to be, a party. In the event a
registration is postponed or sales by a Participating Holder pursuant to an
effective Registration Statement are suspended in accordance with this
paragraph, there shall be added to the period during which the REIT is obligated
to keep a Registration Statement effective the number of days for which the
Registration Statement was postponed or sales were suspended.

        4.      Expenses of Registration. The REIT will pay all Registration
Expenses of all registrations under this Agreement. For purposes of this
Agreement, the term "Registration Expenses" shall mean all expenses incurred by
the REIT in complying with this Agreement, including without limitation, all
registration and filing fees, exchange listing fees, printing expenses, the fees
and disbursements of counsel for the REIT and the reasonable fees and
disbursements of one counsel selected by the Participating Holders, the fees and
disbursements of the REIT's accountants, state Blue Sky fees and expenses, and
the expense of any special audits incident to or required by any such
registration, but excluding underwriting discounts and selling commissions.

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        5.      Indemnification.

                (a)     Indemnification of Participating Holders. In the event
of any registration of any of the Registrable Shares under the Securities Act
pursuant to this Agreement, the REIT will indemnify and hold harmless each
Participating Holder, each of its directors and officers and each other person,
if any, who controls such Participating Holder within the meaning of the
Securities Act or the Exchange Act, against any losses, claims, damages or
liabilities to which such Participating Holder or controlling person may become
subject under the Securities Act, the Exchange Act, Blue Sky laws or otherwise,
insofar as such losses, claims, damages or liabilities (or actions in respect
thereof) arise out of or are based upon any untrue statement or alleged untrue
statement of any material fact contained in any Registration Statement under
which such Registrable Shares were registered under the Securities Act, any
preliminary prospectus or final prospectus contained in the Registration
Statement, or any amendment or supplement to such Registration Statement, or
arise out of or are based upon the omission or alleged omission to state a
material fact required to be stated therein or necessary to make the statements
therein, in light of the circumstances in which they were made, not misleading;
and the REIT will reimburse such Participating Holder and each such controlling
person for any legal or any other expenses reasonably incurred by such
Participating Holder or controlling person in connection with investigating or
defending any such loss, claim, damage, liability or action; provided, however,
that the REIT will not be liable in any such case to the extent that any such
loss, claim, damage or liability arises out of or is based upon any untrue
statement or omission made in such Registration Statement, preliminary
prospectus or prospectus, or any such amendment or supplement, in reliance upon
and in conformity with information furnished to the REIT, in writing, by or on
behalf of any Participating Holder or controlling person specifically for use in
the preparation thereof; and provided further, however, that any indemnification
contained in this paragraph with respect to any preliminary prospectus shall not
inure to the benefit of any person who otherwise is entitled to indemnification
hereunder on account of any loss, liability, claim, damage or expense if a copy
of an amended or supplemental preliminary prospectus, or the final prospectus,
shall have been delivered or sent to such person within the time required by the
Securities Act, and the untrue statement or omission of a material fact was
corrected in such amended or supplemental preliminary prospectus or final
prospectus and provided that such person did not deliver such amended or
supplemental preliminary prospectus or final prospectus on a timely basis.

                (b)     Indemnification of the REIT. In the event of any
registration of any of the Registrable Shares under the Securities Act pursuant
to this Agreement, each Participating Holder will indemnify and hold harmless
the REIT, each of its directors and officers and each person, if any, who
controls the REIT within the meaning of the Securities Act or the Exchange Act,
against any losses, claims, damages or liabilities, joint or several, to which
the REIT, such directors and officers or controlling persons may become subject
under the Securities Act, Exchange Act, Blue Sky laws or otherwise, insofar as
such losses, claims, damages or liabilities (or actions in respect thereof)
arise out of or are based upon any untrue statement or alleged untrue statement
of a material fact contained in any Registration Statement under which such
Registrable Shares were registered under the Securities Act, any preliminary
prospectus or final prospectus contained in the Registration Statement, or any
amendment or

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supplement to the Registration Statement, or arise out of or are based upon any
omission or alleged omission to state a material fact required to be stated
therein or necessary to make the statements therein, in light of the
circumstances in which they were made, not misleading, in each case only if such
statement or omission was made in reliance upon and in conformity with
information furnished in writing to the REIT by or on behalf of such
Participating Holder or controlling person, specifically for use in connection
with the preparation of such Registration Statement, prospectus, amendment or
supplement. No Participating Holder shall be liable pursuant to this Section
5(b) for any amount in excess of the proceeds of the offering received by such
Participating Holder.

                (c)     Notice of Claim. Each party entitled to indemnification
under this Section 5 (the "Indemnified Party") shall give notice to the party
required to provide indemnification (the "Indemnifying Party") promptly after
such Indemnified Party has actual knowledge of any claim as to which indemnity
may be sought, and shall permit the Indemnifying Party to assume the defense of
any such claim or any litigation resulting therefrom; provided that counsel for
the Indemnifying Party, who shall conduct the defense of such claim or
litigation, shall be approved by the Indemnified Party (whose approval shall not
be unreasonably withheld); and, provided, further, that the failure of any
Indemnified Party to give notice as provided herein shall not relieve the
Indemnifying Party of its obligations under this Section 5 unless the failure to
provide such notice materially prejudices the defense by the Indemnifying Party
against such claim. The Indemnified Party may participate in such defense at
such party's expense (provided that the counsel of the Indemnifying Party shall
control the defense of such claim or proceeding); provided, however, that the
Indemnifying Party shall pay such expense if representation of such Indemnified
Party by the counsel retained by the Indemnifying Party would, in the opinion of
counsel of the Indemnified Party, be inappropriate due to actual or potential
differing interests between the Indemnified Party and any other party
represented by such counsel in such proceeding, it being understood, however,
that in such event, the Indemnifying Party shall be liable for the reasonable
fees and expenses of only one counsel for the Indemnified Parties. No
Indemnifying Party, in the defense of any such claim or litigation shall as to
an Indemnified Party, except with the consent of such Indemnified Party, consent
to entry of any judgment or enter into any settlement which does not include as
an unconditional term thereof the giving by the claimant or plaintiff to such
Indemnified Party of a release from all liability in respect of such claim or
litigation, and no Indemnified Party shall consent to entry of any judgment or
settle such claim or litigation without the prior written consent of the
Indemnifying Party.

        6.      Rule 144. The REIT covenants that it will file the reports
required to be filed by it under the Securities Act and the Exchange Act and the
rules and regulations adopted by the Commission thereunder (or, if the REIT is
not required to file such reports, it will, upon the request of the holders of
the Registrable Securities, make publicly available such information as
necessary to permit sales pursuant to Rule 144 under the Securities Act) and it
will do all such other acts and things from time to time as reasonably requested
by the holders of the Registrable Securities to the extent required from time to
time to enable the holders of the Registrable Shares to sell Registrable Shares
without registration under the Securities Act within the limitation of the
exemptions provided by Rule 144 under the Securities Act, as such Rule may be
amended from time to time, or any similar rule or regulation hereunder adopted
by the Commission.

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        7.      Cooperation. The Holders shall furnish to the REIT such
information regarding the Holders and the distribution proposed by Participating
Holders as the REIT may from time to time reasonably request in writing, and
shall do such reasonable acts and things as the REIT may from time to time
request, with respect to any registration, qualification or compliance referred
to in this Agreement and in order to permit the REIT to comply with the
requirements of law. Any failure by a Holder to make available such information
or to do such acts and things shall constitute a waiver by such Holder of its
rights to include such Holder's Registrable Shares in any such registration.

        8.      Restriction on Resale. Unless otherwise agreed by the REIT,
until the date on which there are no Registrable Shares, each Holder agrees that
it will not resell such Registrable Shares without registration under the
Securities Act, compliance with Rule 144 under the Securities Act or an opinion
of counsel for such Holder reasonably acceptable to the REIT, addressed to the
REIT, to the effect that no such registration is required. All reasonable costs,
fees and expenses of counsel in connection with such opinion shall be borne by
the REIT.

        9.      Lock-Up Agreement. In consideration of the REIT's agreement to
provide the Holders with the registration rights as set forth in this Agreement,
Klaff agrees with the REIT and the Partnership that it will not for a period of
five (5) years commencing on the Closing Date or such lesser period if permitted
pursuant to the Contribution Agreement (the "Lock-Up Period") (i) sell, assign,
or otherwise transfer the Units to be issued at the Closing or (ii) convert any
Units into Conversion Shares. Notwithstanding the foregoing, the aforementioned
prohibition shall not apply to (a) a transfer of Units (which shall nonetheless
comply with any requirements or conditions to transfer in the Partnership
Agreement of the Partnership) to a Permitted Transferee; or (b) bona fide pledge
of Units (provided that the pledgee agrees to be bound by the terms of this
Agreement as if an original signatory thereto). For purposes of this Section 10,
the term "Permitted Transferees" means (i) any partner or other equity owner of
the Partnership or Klaff; (ii) any equity owner of any partner or other equity
owner of the Partnership or Klaff; (iii) members of the Immediate Family (as
defined below) of any person described in (i) or (ii); and (iv) trusts for the
benefit of, or entities controlled by, one or more of the persons described in
(i), (ii) or (iii); and/or (v) any public charity, public foundation or
charitable institution as defined in Section 501(c)(3) of the Internal Revenue
Code of 1986, as amended. For purposes of this Section 10, the term "Immediate
Family" means, with respect to any natural person, such natural person's spouse,
parents, parents-in-law, descendants, nephews, nieces, brothers, sisters,
brothers-in-law, sisters-in-law and children-in-law (including adopted persons).
A transfer to any Permitted Transferee shall not be deemed effective, and the
REIT may issue stop transfer instructions to its transfer agent of the Shares in
connection with a purported transfer, unless and until the transferor shall give
the REIT written notice stating the name and address of the Permitted Transferee
and identifying the securities which are being transferred and the REIT shall
have received the written agreement of the Permitted Transferee to be bound by
the terms of this Agreement as if an original signatory hereto.

        10.     Miscellaneous.

                (a)     Controlling Law. This Agreement shall be governed by and
construed in accordance with the laws of the State of New York.

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                (b)     Notices. All notices and other communications hereunder
shall be in writing and shall be sent by certified mail, postage prepaid, return
receipt requested; by an overnight express courier service that provides written
confirmation of delivery; or by facsimile with written confirmation by the
sending machine or with telephone confirmation of receipt, addressed as follows:

                        (i)     If to REIT or Partnership:

                                Acadia Realty Trust
                                1311 Mamaroneck Avenue, Suite 260
                                White Plains, NY  10605
                                Attention:  Robert Masters, Esq.
                                Telephone:  914-288-8139
                                Facsimile:  914-428-3646
                                Email:      rmasters@acadiarealty.com

                        (ii)    If to Klaff:

                                Klaff Realty, LP
                                122 South Michigan Avenue
                                Chicago, IL  60603
                                Attention:  Hersch M. Klaff
                                Telephone:  312-360-3102
                                Facsimile:  312-360-0606
                                Email: hklaff@klaff.com

                                With a copy to:

                                Allan J. Reich, Esq.
                                Seyfarth Shaw LLP
                                55 E. Monroe Street, Suite 4200
                                Chicago, IL  60603
                                Telephone:  312-781-8650
                                Facsimile:  312-269-8869
                                Email:  areich@seyfarth.com

        Any party may alter the address to which communications or copies are to
be sent by giving notice of such change of address in conformity with the
provisions of this paragraph for the giving of notice. Notices given hereunder
shall be deemed received upon actual receipt thereof or, in the case of notice
by mail, upon two days from the date notice is first deposited in the mail in
the manner provided above

                (a)     Binding Nature of Agreement. This Agreement shall be
binding upon and inure to the benefit of (i) the REIT and its successors and
assigns and (ii) each Holder and its heirs, successors and assigns.

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                (b)     Transfer or Assignment of Registration Rights. Subject
to Section 10 hereof, the rights with respect to any Registrable Shares to cause
the REIT to register such securities granted to a Holder by the REIT under this
Agreement may be transferred or assigned by a Holder, in whole or in part, to a
transferee or assignee of any Registrable Shares (or any Units which are
convertible, exercisable or redeemable, directly or indirectly, for Registrable
Shares); provided that, in such case, the REIT shall be given written notice
stating the name and address of said transferee or assignee and identifying the
securities with respect to which such registration rights are being transferred
or assigned and the REIT shall have received the written agreement of such
transferee or assignee to be bound by the terms of this Agreement.

                (c)     Execution in Counterparts. This Agreement may be
executed in any number of counterparts, each of which shall be deemed to be an
original as against any party whose signature appears thereon, and all of which
shall together constitute one and the same instrument. This Agreement shall
become binding when one or more counterparts hereof, individually taken
together, shall bear the signatures of all of the parties reflected hereon as
the signatories.

                (d)     Provisions Separable. The provisions of this Agreement
are independent of and separable from each other, and no provision shall be
affected or rendered invalid or unenforceable by virtue of the fact that for any
reason any other or others of them may be invalid or unenforceable in whole or
in part.

                (e)     Entire Agreement. This Agreement contains the entire
understanding among the parties hereto with respect to the subject matter
hereof, and supersedes all prior and contemporaneous agreements and
understandings, inducements or conditions, express or implied, oral or written,
except as herein contained. This Agreement may not be modified or amended other
than by an agreement in writing.

                (f)     Paragraph Headings. The paragraph headings in this
Agreement are for convenience only; they form no part of this Agreement and
shall not affect its interpretation.

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        IN WITNESS WHEREOF, the parties executed and delivered this Agreement on
the date first above written.


                                ACADIA REALTY TRUST

                                By:
                                    --------------------------------------------
                                Name:
                                Title:


                                ACADIA REALTY LIMITED PARTNERSHIP

                                By:   Acadia Realty Trust,
                                      its General Partner

                                      By:
                                          --------------------------------------
                                      Name:
                                      Title:

                                KLAFF REALTY, LP

                                BY:   KLAFF REALTY, LIMITED, ITS GENERAL PARTNER

                                      By:
                                          --------------------------------------
                                               Hersch M. Klaff, President

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