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                                                      REGISTRATION NO. 333-47858

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                                 ---------------

                         POST-EFFECTIVE AMENDMENT NO. 1

                                       TO
                                    FORM S-3
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                                 ---------------

                             USINTERNETWORKING, INC.
             (Exact name of Registrant as specified in its charter)

     DELAWARE                  ONE USi PLAZA                    43-1570294
  (State or other      ANNAPOLIS, MARYLAND 21401-7478        (I.R.S. Employer
  jurisdiction of              (410) 897-4400             Identification Number)
 incorporation or
   organization)

       (Address, including zip code, and telephone number, including
            area code, of Registrant's principal executive offices)

                             WILLIAM T. PRICE, ESQ.
                 VICE PRESIDENT, SECRETARY AND GENERAL COUNSEL
                                 ONE USi PLAZA
                         ANNAPOLIS, MARYLAND 21401-7478
                                 (410) 897-4400

                (Name, address, including ZIP code, and telephone
               number, including area code, of agent for service)
                                 ---------------

                                   COPIES TO:
                            JOHN D. WATSON, JR., ESQ.
                                LATHAM & WATKINS
                      555 ELEVENTH STREET, N.W., SUITE 1000
                                   WASHINGTON,
                                   D.C. 20004
                                 (202) 637-2200


     APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: From time
to time after the effective date of this Registration Statement, as determined
by the Registrant.

     If the only securities being registered on this Form are being offered
pursuant to dividend or interest reinvestment plans, please check the following
box. [ ]

     If any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, other than securities offered only in connection with dividend or interest
reinvestment plans, check the following box. [X]

     If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act of 1933, please check the
following box and list the Securities Act registration statement number of the
earlier effective registration statement for the same offering. [ ]

     If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act of 1933, check the following box and list the
Securities Act registration statement number of the earlier effective
registration statement for the same offering. [ ]

     If delivery of the prospectus is expected to be made pursuant to Rule 434
under the Securities Act of 1933, please check the following box. [ ]

     THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION
STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(A) OF
THE SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME
EFFECTIVE ON SUCH DATE AS THE SECURITIES AND EXCHANGE COMMISSION, ACTING
PURSUANT TO SAID SECTION 8(A), MAY DETERMINE.

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PROSPECTUS

                                   [USI LOGO]
                             USinternetworking, INC.
                      BY THIS PROSPECTUS WE MAY OFFER UP TO
                        $150,000,000 OF OUR COMMON STOCK

                    -----------------------------------------


     This prospectus will allow us to issue common stock over time. This means:

     -    we will provide a prospectus supplement each time we issue common
          stock;

     -    the prospectus supplement will inform you about the specific terms of
          that offering and also may add, update or change information contained
          in this document;

     -    you should read this document and any prospectus supplement carefully
          before you invest; and

     -    this prospectus may not be used to offer or sell the common stock
          unless accompanied by a prospectus supplement.

     Our common stock is quoted on The Nasdaq National Market under the symbol
"USIX." On June 15, 2001, the last reported sale price of the common stock was
$1.30 per share.

                    -----------------------------------------


INVESTING IN OUR COMMON STOCK INVOLVES SUBSTANTIAL RISKS. SEE "RISK FACTORS" ON
PAGE 6.

                    -----------------------------------------


     NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES
COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR PASSED UPON THE
ADEQUACY OR ACCURACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.

                  The date of this prospectus is June 18, 2001



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                                TABLE OF CONTENTS



                                                                            PAGE
                                                                            ----
                                                                         
Summary ...................................................................   4
Risk Factors ..............................................................   6
Special Note Regarding Forward-Looking Statements
  Contained in this Prospectus ............................................   6
Use of Proceeds ...........................................................   7
Plan of Distribution ......................................................   8
Experts ...................................................................   11
Legal Matters .............................................................   11
Incorporation of Documents by Reference ...................................   11
Where You Can Find More Information .......................................   11


This prospectus references and depicts certain trademarks, service marks and
trade names of other companies. "USinternetworking," "USi," "Internet Managed
Application Provider," "PriorityPeering, USiView," and IMAP are our registered
trademarks. We have applied for federal registration of the marks "Making
Software Simple," "AppHost," "Global Enterprise Management Center," "USiLink,"
"USiConnects," "USiMirror," "USiAccelerate," "USi Global Services Platform,"
"USiGSP" and "GEMC."

     WE HAVE NOT AUTHORIZED ANY DEALER, SALESPERSON OR OTHER PERSON TO GIVE ANY
INFORMATION OR TO MAKE ANY REPRESENTATION OTHER THAN THOSE CONTAINED OR
INCORPORATED BY REFERENCE IN THIS PROSPECTUS AND ANY ACCOMPANYING PROSPECTUS
SUPPLEMENT. YOU MUST NOT RELY UPON ANY INFORMATION OR REPRESENTATION NOT
CONTAINED OR INCORPORATED BY REFERENCE IN THIS PROSPECTUS OR ANY ACCOMPANYING
PROSPECTUS SUPPLEMENT AS IF WE HAD AUTHORIZED IT. THIS PROSPECTUS AND ANY
ACCOMPANYING PROSPECTUS SUPPLEMENT DO NOT CONSTITUTE AN OFFER TO SELL OR THE
SOLICITATION OF AN OFFER TO BUY ANY SECURITIES OTHER THAN THE REGISTERED
SECURITIES TO WHICH THEY RELATE, NOR DOES THIS PROSPECTUS AND ANY ACCOMPANYING
PROSPECTUS SUPPLEMENT CONSTITUTE AN OFFER TO SELL OR THE SOLICITATION OF AN
OFFER TO BUY SECURITIES IN ANY JURISDICTION TO ANY PERSON TO WHOM IT IS UNLAWFUL
TO MAKE SUCH OFFER OR SOLICITATION IN SUCH JURISDICTION. YOU SHOULD NOT ASSUME
THAT THE INFORMATION CONTAINED IN THIS PROSPECTUS AND ANY ACCOMPANYING
PROSPECTUS SUPPLEMENT IS CORRECT ON ANY DATE AFTER THEIR RESPECTIVE DATES, EVEN
THOUGH THIS PROSPECTUS OR ANY PROSPECTUS SUPPLEMENT IS DELIVERED OR SECURITIES
ARE SOLD ON A LATER DATE.





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                                     SUMMARY

                              ABOUT THIS PROSPECTUS

     This prospectus is part of a registration statement that we filed with the
Securities and Exchange Commission using a "shelf" registration process. Under
this shelf process, we may from time to time sell any number of the shares of
common stock in one or more offerings up to a total aggregate dollar value of
$150,000,000.

     Each time we sell shares of common stock, we will provide a prospectus
supplement that will contain specific information about the terms of that
offering. The prospectus supplement may also add, update or change information
contained in this prospectus. You should read both this prospectus and any
prospectus supplement together with the additional information described below
under the heading "Where You Can Find More Information."

     The registration statement that contains this prospectus, including the
exhibits to the registration statement and the information incorporated by
reference, contains additional information about the common stock offered under
this prospectus. That registration statement can be read at the Securities and
Exchange Commission, or SEC, web site or at the SEC offices mentioned below
under the heading "Where You Can Find More Information."

     You should rely only on the information provided in this prospectus and in
any prospectus supplement, including the information incorporated by reference.
We have not authorized anyone to provide you with different information. You
should not assume that the information in this prospectus, or any supplement to
this prospectus, is accurate at any date other than the date indicated on the
cover page of these documents.


                               PROSPECTUS SUMMARY

     This summary highlights information contained elsewhere in this prospectus.
It is not complete, and does not contain all the information you should consider
before investing in our common stock. To fully understand this offering and its
consequences to you, you should read the entire prospectus carefully, including
the "Risk Factors" section, the "Special Note Regarding Forward-Looking
Statements Contained in this Prospectus" and the financial data and the
documents that we incorporate by reference into this prospectus.

                                USinternetworking

     USi was established in 1998 as a full service, enterprise Application
Service Provider (ASP) delivering the functionality of complex enterprise
software as a service. "Full Service" means we take total responsibility for
delivering the latest enterprise, e-business, and managed web hosting solutions
over our proprietary Global Service Platform (SM) (GSP SM). Our GSP environment
is designed specifically to provide superior performance for ASP solutions. Our
GSP environment is located in secure, fully redundant data centers that we
control and operate and from which our technicians and engineers provide 24 by 7
monitoring and support. Our ASP services are primarily delivered as Internet
Managed Applications Provider (SM) (iMAP SM) offerings, which seamlessly
integrate the hardware and software, networking and security, and 24 by 7 Client
Care we provide to our clients. We also back our iMAP offerings with some of the
highest service level guarantees in the industry. Our full service,
comprehensive approach enables our clients' organizations to gain the
competitive advantage of advanced applications and web-based technologies,
without having to divert time and resources from their core businesses.

     We offer a full range of complementary value-added services designed to
satisfy the rapidly evolving requirements in the ASP market. Our iMAP offerings
encompass enterprise application services and e-business services, and typically
include application consulting and integration as well as managed hosting and
ongoing support. We also offer stand-alone consulting services. Our iMAP
contracts usually provide for a modest up-front payment and are generally not
less than three years in length. Our iMAP contracts usually provide for payment
reductions in the event that agreed upon service levels, as measured and
quantified by system performance benchmarks, are not met.

     We introduced our iMAP services in late 1998. For the year ended December
31, 2000, we generated $109.5 million in revenues. As of December 30, 2000, we
had 233 signed contracts with 168 clients for our iMAP services. The total
expected revenue from these contracts, assuming payment over the full contract
terms, exceeds $354.0 million.


   Our executive offices are located at One USi Plaza, Annapolis, Maryland
21401-7478; and our telephone number is (410) 897-4400.

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                                  RISK FACTORS

     Before you decide whether to purchase any of our securities, in addition to
the other information in this prospectus, you should carefully consider the risk
factors set forth under the heading "Risk Factors" in the section entitled
"Management's Discussion and Analysis of Financial Condition and Results of
Operations" in our most recent Annual Report on Form 10-K, which is incorporated
by reference into this prospectus, as the same may be updated from time to time
by our future filings under the Securities Exchange Act. For more information,
see the section entitled "Incorporation by Reference."


                SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS
                          CONTAINED IN THIS PROSPECTUS

     This prospectus includes or incorporates by reference forward-looking
statements within the meaning of Section 27A of the Securities Act of 1933 and
Section 21E of the Securities Exchange Act of 1934. These statements relate to
future events or our future clinical or product development or financial
performance. In some cases, you can identify forward-looking statements by
terminology such as "may," "will," "should," "expects," "plans," "anticipates,"
"believes," "estimates," "predicts," "potential" or "continue" or the negative
of those terms and other comparable terminology.

     These statements reflect only management's current expectations. Important
factors that could cause actual results to differ materially from the
forward-looking statements we make or incorporate by reference in this
prospectus are set forth under the heading "Risk Factors" in the section
entitled "Management's Discussion and Analysis of Financial Condition and
Results of Operations" in our most recent Annual Report on Form 10-K, as may be
updated from time to time by our future filings under the Securities Exchange
Act, and elsewhere in the documents incorporated by reference in this
prospectus. If one or more of these risks or uncertainties materialize, or if
any underlying assumptions prove incorrect, our actual results, performance or
achievements may vary materially from any future results, performance or
achievements expressed or implied by these forward-looking statements. We
undertake no obligation to publicly update any forward-looking statements,
whether as a result of new information, future events or otherwise.


                                 USE OF PROCEEDS

   We cannot guarantee that we will receive any proceeds in connection with this
offering.

   We intend to use the net proceeds of this offering, if any, for general
corporate purposes, including working capital to fund anticipated operating
losses, expenses and capital expenditures. As of the date of this prospectus, we
cannot specify with certainty the particular uses for the net proceeds, if any,
to be received upon consummation of this offering. Accordingly, our management
will have broad discretion in the application of any net proceeds received.
Pending such uses, we intend to invest the net proceeds, if any, from this
offering in short-term, interest-bearing, investment grade securities.



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                              PLAN OF DISTRIBUTION

GENERAL

     We may sell the securities from time to time pursuant to underwritten
public offerings, negotiated transactions, block trades or a combination of
these methods. The securities also may be sold pursuant to what is known as an
equity line of credit, as described below under the heading "Equity Line of
Credit." We may sell the securities (1) through underwriters or dealers, (2)
through agents, and/or (3) directly to one or more purchasers. We may distribute
the securities from time to time in one or more transactions at:

     -    a fixed price or prices, which may be changed;

     -    market prices prevailing at the time of sale;

     -    prices related to the prevailing market prices; or

     -    negotiated prices.

     We may solicit directly offers to purchase the securities being offered by
this prospectus. We may also designate agents to solicit offers to purchase the
securities from time to time. We will name in a prospectus supplement any agent
involved in the offer or sale of our securities.

     If we utilize a dealer in the sale of the securities being offered by this
prospectus, we will sell the securities to the dealer, as principal. The dealer
may then resell the securities to the public at varying prices to be determined
by the dealer at the time of resale.

     If we utilize an underwriter in the sale of the securities being offered by
this prospectus, we will execute an underwriting agreement with the underwriter
at the time of sale and we will provide the name of any underwriter in the
prospectus supplement which the underwriter will use to make resales of the
securities to the public. In connection with the sale of the securities, we, or
the purchasers of securities for whom the underwriter may act as agent, may
compensate the underwriter in the form of underwriting discounts or commissions.
The underwriter may sell the securities to or through dealers, and the
underwriter may compensate those dealers in the form of discounts, concessions
or commissions.

     In the event we enter into an agreement regarding an equity line of credit,
other than as described below, which contemplates an at the market equity
offering, we will file a post-effective amendment to this registration statement
that identifies the underwriter(s) in that at the market equity offering.

     With respect to underwritten public offerings, negotiated transactions and
block trades, we will provide in the applicable prospectus supplement any
compensation we pay to underwriters, dealers or agents in connection with the
offering of the securities, and any discounts, concessions or commissions
allowed by underwriters to participating dealers. Underwriters, dealers and
agents participating in the distribution of the securities may be deemed to be
underwriters within the meaning of the Securities Act of 1933, as amended, and
any discounts and commissions received by them and any profit realized by them
on resale of the securities may be deemed to be underwriting discounts and
commissions. We may enter into agreements to indemnify underwriters, dealers and
agents against civil liabilities, including liabilities under the Securities
Act, or to contribute to payments they may be required to make in respect
thereof.

     Shares of common stock sold pursuant to the registration statement of which
this prospectus is a part will be authorized for quotation and trading on the
Nasdaq National Market. Other securities may or may not be listed on the Nasdaq
National Market or a national securities exchange. To facilitate the offering of
securities, other than securities offered through an equity line of credit,
certain persons participating in the offering may engage in transactions that
stabilize, maintain or otherwise affect the price of the securities. This may
include over-allotments or short sales of the securities, which involve the sale
by persons participating in the offering of more securities than we sold to
them. In these circumstances, these persons would cover such over-allotments or
short positions by making purchases in the open market or by exercising their
over-allotment option. In addition, these persons may stabilize or maintain the
price of the securities by bidding for or purchasing securities in the open
market or by imposing penalty bids, whereby selling concessions allowed to
dealers participating in the offering may be reclaimed if securities sold by
them are repurchased in connection with stabilization

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transactions. The effect of these transactions may be to stabilize or maintain
the market price of the securities at a level above that which might otherwise
prevail in the open market. These transactions may be discontinued at any time.

     The underwriters, dealers and agents may engage in other transactions with
us, or perform other services for us, in the ordinary course of their business.

EQUITY LINE OF CREDIT

     On November 13, 2000 we entered into what is sometimes termed an equity
line of credit arrangement with Acqua Wellington North American Equities Fund,
Ltd. Specifically, we entered into a common stock purchase agreement with Acqua
Wellington, which, as amended and restated, provides that Acqua Wellington is
committed to purchase up to $60,800,000 of our common stock over the 28-month
term of the purchase agreement. We have filed the purchase agreement as an
exhibit to this registration statement. The total amount of securities available
under the purchase agreement, as amended and restated, does not exceed 10% of
the aggregate market value of our outstanding common stock that was held by
non-affiliates within sixty days prior to November 13, 2000. From time to time
beginning in November 2000 and ending on or before October 2003 and at our sole
discretion, we may present Acqua Wellington with draw down notices constituting
offers to purchase our common stock over 18 consecutive trading days or such
other number of trading days as agreed upon by us and Acqua Wellington. Under
the purchase agreement, we are able to present Acqua Wellington with up to 24
draw down notices during the term of the agreement, with a minimum of five
trading days required between each draw down period.

     Once presented with a draw down notice, Acqua Wellington is required to
purchase a pro rata portion of the shares on each trading day during the trading
period on which the daily volume weighted average price for our common stock
exceeds a threshold price for such draw down determined by us and set forth in
the draw down notice. The per share purchase price for these shares equals the
daily volume weighted average price of our common stock on each date during the
draw down period on which shares are purchased, less a discount ranging from
4.0% to 6.5%, based on our market capitalization on the date we issue the draw
down notice. If the daily volume weighted average price of our common stock
falls below the threshold price on any trading day during a draw down period,
the purchase agreement provides that Acqua Wellington will not be required to
purchase the pro-rata portion of shares of common stock allocated to that day.
However, at its election, Acqua Wellington could buy the pro-rata portion of
shares allocated to that day at the threshold price less the discount described
above.

     The purchase agreement also provides that from time to time and at our sole
discretion we may grant Acqua Wellington the right to exercise one or more call
options to purchase additional shares of our common stock during each draw down
pricing period for the amount that we specify. Upon Acqua Wellington's exercise
of the call option, we will issue and sell the shares of our common stock
subject to the call option at a price equal to the greater of the daily volume
weighted average price of our common stock on the day Acqua Wellington notifies
us of its election to exercise its call option or the threshold price for the
call option determined by us and set forth in the draw down notice, less a
discount ranging from 4.0% to 6.5%, based on our market capitalization on the
date we issue the draw down notice.

     In addition to our issuance of shares of common stock to Acqua Wellington
pursuant to the purchase agreement, this prospectus also covers the sale of
those shares from time to time by Acqua Wellington to the public. Acqua
Wellington is an "underwriter" within the meaning of Section 2(a)(11) of the
Securities Act.

     Acqua Wellington has informed us that it intends to use Carlin Equities
Corp. as the broker-dealer to sell shares of common stock on the Nasdaq National
Market. Such sales will be made on the Nasdaq National Market at prices and at
terms then prevailing or at prices related to the then current market price.
Carlin Equities Corp. is the same broker-dealer that Acqua Wellington used to
effectuate sales, if any, of the shares of common stock it purchased from us in
February 2001 pursuant to the draw down notice we delivered in January 2001.
Carlin Equities Corp. is an underwriter within the meaning of Section 2(a)(11)
of the Securities Act. We filed prospectus supplements to our registration
statement no. 333-47858 on February 15, 2001 and according to a telephone
interpretation issued by the SEC Staff, we should have filed a post-effective
amendment to that registration statement naming Acqua Wellington and Carlin
Equities Corp. as underwriters. Acqua Wellington has informed us that Carlin
Equities Corp., which is not an affiliate of Acqua Wellington, will receive
commissions from Acqua Wellington which will not exceed customary brokerage
commissions. Acqua Wellington also will pay other expenses associated with the
sale of the common stock it acquires pursuant to the purchase agreement.

     The shares of common stock may be sold in one or more of the following
manners:


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     -    ordinary brokerage transactions and transactions in which the broker
          solicits purchasers; or

     -    a block trade in which the broker or dealer so engaged will attempt to
          sell the shares as agent, but may position and resell a portion of the
          block as principal to facilitate the transaction.

     Acqua Wellington has agreed that prior to, during the term of the purchase
agreement, neither Acqua Wellington nor any of its affiliates will, directly or
indirectly, sell any of our securities except the shares that it owns or has the
right to purchase pursuant to the provisions of a draw down notice. Acqua
Wellington has agreed that it will not enter into a short position with respect
to shares of our common stock except that Acqua Wellington may sell shares that
it has not yet taken delivery of pursuant to the provisions of a draw down
notice so long as Acqua Wellington covers any such sales with the shares
purchased pursuant to such draw down notice. Acqua Wellington has further agreed
that it will not grant any option to purchase or acquire any right to dispose or
otherwise dispose for value of any shares of our common stock or any securities
convertible into, or exchangeable for, or warrants to purchase, any shares of
our common stock, or enter into any swap, hedge or other agreement that
transfers, in whole or in part, the economic risk of ownership of our common
stock, except for the sales permitted by the purchase agreement. Acqua
Wellington also has agreed that its sales of our common stock on any trading day
will not represent more than 30% of the total trading volume of our common stock
for that trading day.

     In addition, Acqua Wellington and Carlin Equities Corp. will be subject to
liability under the federal securities laws and must comply with the
requirements of the Securities Act and the Securities Exchange Act of 1934, as
amended, including without limitation, Rule 415(a)(4) under the Securities Act
and Rule 10b-5 and Regulation M under the Exchange Act. These rules and
regulations may limit the timing of purchases and sales of shares of common
stock by Acqua Wellington or Carlin Equities Corp. Under these rules and
regulations, Acqua Wellington and Carlin Equities Corp.:

     -    may not engage in any stabilization activity in connection with our
          securities;

     -    must furnish each broker which offers shares of our common stock
          covered by this prospectus with the number of copies of this
          prospectus and any prospectus supplement which are required by each
          broker; and

     -    may not bid for or purchase any of our securities or attempt to induce
          any person to purchase any of our securities other than as permitted
          under the Exchange Act.

These restrictions may affect the marketability of the shares of common stock by
Acqua Wellington and Carlin Equities Corp.

     We have agreed to indemnify and hold harmless Acqua Wellington and Carlin
Equities Corp. against certain liabilities, including liabilities under the
Securities Act, which may be based upon, among other things, any untrue
statement or alleged untrue statement of a material fact contained in or
incorporated by referenced in the registration statement of which this
prospectus is a part, or any omission or alleged omission to state in the
registration statement or any document incorporated by reference in the
registration statement, a material fact required to be stated therein or
necessary to make the statements therein not misleading, unless made or omitted
in reliance upon written information provided to us by Acqua Wellington or
Carlin Equities Corp. We have agreed to pay twenty five thousand dollars
($25,000) of Acqua Wellington's reasonable attorneys' fees and expenses
(exclusive of disbursements and out-of-pocket expenses) incurred by Acqua
Wellington in connection with the preparation, negotiation, execution and
delivery of the purchase agreement. We have also agreed to pay all reasonable
fees and expenses incurred by Acqua Wellington in connection with any
amendments, modifications or waivers of the purchase agreement.

     The purchase agreement as executed and as amended and restated as of
November 13, 2000 has been incorporated by reference into and has been filed as
an exhibit to this registration statement.





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                                     EXPERTS

     Ernst & Young LLP, independent auditors, have audited our consolidated
financial statements and schedule and the consolidated financial statements of
I.I.T. Holdings, Inc. and subsidiaries included in our Annual Report on Form
10-K for the year ended December 31, 2000, as set forth in their reports, which
are incorporated by reference in this prospectus and elsewhere in the
registration statement. Our financial statements and schedule are incorporated
by reference in reliance on Ernst & Young LLP's reports, given on their
authority as experts in accounting and auditing.

                                  LEGAL MATTERS

     The validity of the issuance of common stock offered in this prospectus
will be passed upon for USi by Latham & Watkins, Washington, D.C. Partners of
Latham & Watkins own in total shares of our common stock representing less than
1% of the total number of shares of common stock outstanding.

                     INCORPORATION OF DOCUMENTS BY REFERENCE

     The Commission allows us to incorporate by reference the information
contained in documents that we file with them. This means that we can disclose
important information to you by referring you to those documents. The
information incorporated by reference is considered to be part of this
prospectus. Information in this prospectus supercedes information incorporated
by reference that we filed with the Commission prior to the date of this
prospectus, while information that we file later with the Commission will
automatically update and supercede this information. We incorporate by reference
the documents listed below and any future filings we will make with the
Commission under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange
Act of 1934:

     -    Our Annual Report on Form 10-K for the fiscal year ended December 31,
          2000, filed on April 2, 2001, including all material incorporated by
          reference therein;

     -    Our Quarterly Report on Form 10-Q for the quarter ended March 31,
          2001, filed on May 15, 2001, including all material incorporated by
          reference therein;

     -    Our Current Reports on Form 8-K, dated January 17, 2001 and May 31,
          2001; and

     -    The description of our common stock contained in our registration
          statement on Form 8-A filed on April 8, 1999.

                       WHERE YOU CAN FIND MORE INFORMATION

     We are currently subject to the periodic reporting and other requirements
of the Securities Exchange Act of 1934. You may read and copy any document we
file or incorporate by reference into this prospectus at the Commission's public
reference rooms located at 450 5th Street, N.W., Washington, D.C. 20549. Please
call the Commission at 1-800-SEC-0330 for further information on the public
reference rooms. Our Commission filings are also available to the public from
commercial document retrieval services and at the web site maintained by the
Commission at: http://www.sec.gov. Our common stock trades on The Nasdaq
National Market.

     You may request a copy of any of this information, at no cost, by writing
or telephoning us at the following address or phone number:

                             USinternetworking, Inc.
                                  One USi Plaza
                         Annapolis, Maryland 21401-7478
                                 (410) 897-4400




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                             USinternetworking, INC.

                                   [USI LOGO]









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                     INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 14.  OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION

     Set forth below is an estimate of the amount of fees and expenses to be
incurred in connection with the issuance and distribution of the Notes and
common stock registered under this prospectus:


                                                         
                    SEC Registration Fee                    $ 39,600
                    Printing and Mailing Costs                10,000
                    Legal Fees and Expenses                   50,000
                    Accounting Fees and Expenses              10,000
                    Reimbursement to Acqua Wellington         25,000
                    Miscellaneous expenses                     5,000
                                                            --------
                    Total                                   $114,600
                                                            ========


ITEM 15. LIMITATION OF LIABILITY AND INDEMNIFICATION

     Section 145 of the General Corporation Law of the State of Delaware
("Section 145") permits a Delaware corporation to indemnify any person who was
or is a party or is threatened to be made a party to any threatened, pending, or
completed action, suit, or proceeding, whether civil, criminal, administrative,
or investigative (other than an action by or in the right of the corporation) by
reason of the fact that such person is or was a director, officer, employee, or
agent of the corporation, or is or was serving at the request of the corporation
as a director, officer, employee, or agent of another corporation, partnership,
joint venture, trust, or other enterprise, against expenses (including
attorneys' fees), judgments, fines, and amounts paid in settlement actually and
reasonably incurred by such person in connection with such action, suit, or
proceeding if such person acted in good faith and in a manner such person
reasonably believed to be in or not opposed to the best interests of the
corporation, and, with respect to any criminal action or proceeding, had no
reasonable cause to believe such person's conduct was unlawful.

     In the case of an action by or in the right of the corporation, Section 145
permits the corporation to indemnify any person who was or is a party or is
threatened to be made a party to any threatened, pending, or completed action or
suit by or in the right of the corporation to procure a judgment in its favor by
reason of the fact that such person is or was a director, officer, employee or
agent of the corporation, or is or was serving at the request of the corporation
as a director, officer, employee or agent of another corporation, partnership,
joint venture, trust or other enterprise against expenses (including attorneys'
fees) actually and reasonably incurred by such person in connection with the
defense or settlement of such action or suit if he acted in good faith and in a
manner such person reasonably believed to be in or not opposed to the best
interest of the corporation. No indemnification may be made in respect of any
claim, issue, or matter as to which such person shall have been adjudged to be
liable to the corporation unless and only to the extent that the Court of
Chancery or the court in which such action or suit was brought shall determine
upon application that, despite the adjudication of liability but in view of all
the circumstances of the case, such person is fairly and reasonably entitled to
indemnity for such expenses which the Court of Chancery or such other court
shall deem proper.

     To the extent that a present or former director or officer of a corporation
has been successful on the merits or otherwise in defense of any action, suit or
proceeding referred to in the preceding two paragraphs, Section 145 requires
that such person be indemnified against expenses (including attorneys' fees)
actually and reasonably incurred by such person in connection therewith.

     Section 145 provides that expenses (including attorneys' fees) incurred by
an officer or director in defending any civil, criminal, administrative, or
investigative action, suit or proceeding may be paid the corporation in advance
of the final disposition of such action, suit or proceeding upon receipt of an
undertaking by or on behalf of such director or officer to repay such amount if
it shall ultimately be determined that such person is not entitled to be
indemnified by the corporation as authorized in Section 145.

     The Company's Certificate provides that an officer or director of the
Company will not be personally liable to the Company or its stockholders for
monetary damages for any breach of his fiduciary duty as an officer or director,
except in certain cases where liability is mandated by the DGCL. The provision
has no effect on any non-monetary remedies that may be available to the Company
or its stockholders, nor does it relieve the Company or its officers or
directors from compliance with federal or state securities laws. The Certificate
also generally provides that the Company shall indemnify, to the fullest extent
permitted by law, any person who was or is a party or is threatened to be made a
party to any threatened, pending or completed action, suit, investigation,
administrative hearing

                                       11
   12

or any other proceeding (each, a "Proceeding") by reason of the fact that he is
or was a director or officer of the Company, or is or was serving at the request
of the Company as a director, officer, employee or agent of another entity,
against expenses incurred by him in connection with such Proceeding. An officer
or director shall not be entitled to indemnification by the Company if (i) the
officer or director did not act in good faith and in a manner reasonably
believed to be in, or not opposed to, the best interests of the Company, or (ii)
with respect to any criminal action or proceeding, the officer or director had
reasonable cause to believe his conduct was unlawful.

     The Bylaws of the Company provide that it shall indemnify any person who is
made a party to any threatened, pending or completed action, suit or proceeding
by reason of the fact that he or she is or was a director or officer of the
Company, and may indemnify any employee or agent of the Company in such
circumstances, against expenses, including attorneys fees, judgments, fines and
amounts paid in settlement actually and reasonably incurred by him or her in
connection with such action, suit or proceeding. No indemnification may be
provided for any person who shall have been finally adjudicated not to have
acted honestly or in the reasonable belief that his or her action was in or not
opposed to the best interests of the Company or who had reasonable cause to
believe that his or her conduct was unlawful. Indemnification must be provided
to any director, officer, employee or agent of the Company to the extent such
person has been successful, on the merits or otherwise, in defense of any action
or claim described above. Any indemnification under this provision of the
Bylaws, unless required under the Bylaws or ordered by a court, can be made only
as authorized in each specific case upon a determination by a majority of
disinterested directors or by independent legal counsel or by the stockholders
that such indemnification is appropriate under the standard set forth in the
preceding sentence.

ITEM 16.  EXHIBITS

(a)   EXHIBITS



                     EXHIBIT
                       NO.                   DESCRIPTION
                     --------       --------------------------------------------

                                 
                       4.1(a)       Second Amended and Restated Certificate of
                                    Incorporation of the Company.

                       4.2(a)       Amended and Restated Bylaws of the Company.


                       4.3(c)       First Amendment to the Company's Second
                                    Amended and Restated Certificate of
                                    Incorporation.

                       4.4(b)       Specimen Certificate for shares of Common
                                    Stock, $.001 par value, of the Company.

                       4.5(*)       Amended and Restated Common Stock Purchase
                                    Agreement Effective as of November 13, 2000
                                    by and between USinternetworking, Inc. and
                                    Acqua Wellington North American Securities
                                    Fund, Ltd.

                       5.1(#)       Opinion of Latham & Watkins with respect to
                                    the validity of the Common Stock.


                      23.1(*)       Consent of Ernst & Young LLP, independent
                                    auditors (regarding the Company's financial
                                    statements).

                      23.2(*)       Consent of Bassan & Associados S.C.,
                                    independent auditors (regarding IIT
                                    financial statements).

                      23.3(*)       Consent of Ernst & Young LLP, independent
                                    auditors (regarding IIT financial
                                    statements).

                      23.5(#)       Consent of Latham & Watkins (included in
                                    Exhibit 5.1).





                                       12
   13



                                 
                      24.1(#)       Powers of Attorney (included on signature
                                    page herein and as previously filed).



*    Filed herewith.

#    Previously filed.

(a)  Incorporated by reference to the Company's Registration Statement on Form
     S-3, as amended (Reg. No. 333-93299).

(b)  Incorporated by reference to the Company's Registration Statement on Form
     S-1, as amended (Reg. No. 333-70717)

(c)  Incorporated by reference to Company's Registration's Statement on Form
     S-1, as amended (Reg. No. 333-95543).

(b)  SCHEDULES

     Schedule II - Valuation of Qualifying Accounts (incorporated by reference
to the Company's Annual Report on Form 10-K for the year ended December 31, 2000
filed by the Company on April 2, 2001.

     All other schedules for which provision is made in the applicable
accounting regulations of the Securities and Exchange Commission are not
required under the related instruction or are inapplicable and have therefore
been omitted.

ITEM 17. UNDERTAKINGS

(a)  The undersigned Registrant hereby undertakes:

     (1)  To file, during any period in which offers or sales are being made, a
          post-effective amendment to this registration statement:

          (i) To include any prospectus required by section 10(a)(3) of the
          Securities Act of 1933;

          (ii) To reflect in the prospectus any facts or events arising after
          the effective date of the registration statement (or the most recent
          post-effective amendment thereof) which, individually or in the
          aggregate, represent a fundamental change in the information set forth
          in the registration statement. However, any increase or decrease in
          volume of securities offered (if the total dollar value of securities
          offered would not exceed that which was registered) and any deviation
          from the low or high end of the estimated maximum offering range may
          be reflected in the form of prospectus filed with the Commission
          pursuant to Rule 424(b) if, in the aggregate, the changes in volume
          and price represent no more than a 20 percent change in the maximum
          aggregate offering price set forth in the "Calculation of Registration
          Fee" table in the effective registration statement; and

          (iii)To include any material information about the plan of
          distribution not previously disclosed in this registration statement
          or any material change to this information in this registration
          statement. However, subparagraphs (i) and (ii) do not apply if the
          information required to be included in a post-effective amendment by
          those paragraphs is contained in the periodic reports filed by the
          Registrant pursuant to Section 13 or Section 15(d) of the Securities
          Exchange Act of 1934 that are incorporated by reference in this
          registration statement;

          provided, however, subparagraphs (a)(1)(i) and (a)(1)(ii) above do not
          apply if the information required to be included in a post-effective
          amendment by those paragraphs is contained in the periodic reports
          filed with or furnished to the SEC by the Registrant pursuant to
          Section 13 or Section 15(d) of the Securities and Exchange Act of 1934
          that are incorporated by reference in this registration statement.

          (2) That, for the purpose of determining any liability under the
     Securities Act of 1933, each such post-effective amendment shall be deemed
     to be a new registration statement relating to the Securities offered
     herein, and the offering of such Securities at that time shall be deemed to
     be the initial bona fide offering thereof.

          (3) To remove from registration by means of a post-effective amendment
     any of the Securities being registered which remain unsold at the
     termination of the offering.

(b)  The undersigned Registrant hereby further undertakes that, for the purposes
     of determining any liability under the Securities Act of 1933, each filing
     of the Registrant's annual report pursuant to Section 13(a) or Section
     15(d) of the Securities Exchange Act of 1934 that is incorporated by
     reference in this registration statement shall be deemed to be a new
     registration

                                       13
   14

     statement relating to the Securities offered herein, and the offering of
     such Securities at that time shall be deemed to be the initial bona fide
     offering thereof.

(c)  Insofar as indemnification for liabilities arising under the Securities Act
     of 1933 may be permitted to directors, officers and controlling persons of
     the Registrant under the provisions of this registration statement, or
     otherwise (other than insurance), the Registrant has been advised that in
     the opinion of the Securities and Exchange Commission such indemnification
     is against public policy as expressed in such Act and is, therefore,
     unenforceable. In the event that a claim for indemnification against such
     liabilities (other than the payment by the Registrant of expenses incurred
     or paid by a director, officer or controlling person of the Registrant in
     the successful defense of any action, suit or proceeding) is asserted by
     such director, officer or controlling person in connection with the
     Securities being registered, the Registrant will, unless in the opinion of
     its counsel the matter has been settled by controlling precedent, submit to
     a court of appropriate jurisdiction the question whether such
     indemnification by it is against public policy as expressed in such Act and
     will be governed by the final adjudication of such issue.




                                       14
   15



Pursuant to the requirements of the Securities Act, the registrant certifies
that it has reasonable grounds to believe that it meets all of the requirements
for filing on Form S-3, and has duly caused this registration statement to be
signed on its behalf by the undersigned, thereunto duly authorized, in the City
of Annapolis, State of Maryland on June 18, 2001.

                                   USINTERNETWORKING, INC.

                                By: /s/ WILLIAM T. PRICE
                                   --------------------------
                                William T. Price
                                Vice President, Secretary
                                and General Counsel

          Pursuant to the requirements of the Securities Act of 1933, the
     registration statement has been signed below on June 18, 2001 by the
     following persons in the capacities indicated.

       SIGNATURE                                     TITLE
           *                            Chairman of the Board
- -----------------------------
  Christopher R. McCleary

           *                            Chief Executive Officer and Director
- -----------------------------
  Andrew A. Stern

           *                            President -E-Commerce Business Unit and
                                        Director
- -----------------------------
  Stephen E. McManus

           *                            Senior Vice President and Chief
                                        Financial Officer
- -----------------------------
  Mark J. McEneaney

                                        Director
- -----------------------------
  R. Dean Meiszer

                                        Director
- -----------------------------
  Benjamin Diesbach

           *                            Director
- -----------------------------
  Ray A. Rothrock

           *                            Director
- -----------------------------
  Frank A. Adams

           *                            Director
- -----------------------------
  William F. Earthman

           *                            Director
- -----------------------------
  John H. Wyant

                                        Director
- -----------------------------
  Joseph R. Zell

           *                            Director
- -----------------------------
  Michael C. Brooks

                                        Director
- -----------------------------
  David J. Poulin

                                        Director
- -----------------------------
  Cathy M. Brienza


  *By: /s/ WILLIAM T. PRICE
  -------------------------
       WILLIAM T. PRICE
       ATTORNEY-IN-FACT




                                       15
   16



                                INDEX TO EXHIBITS



              EXHIBIT
                 NO.                        DESCRIPTION
              --------        --------------------------------------------------
                           
               4.1(a)         Second Amended and Restated Certificate of
                              Incorporation of the Company.

               4.2(a)         Amended and Restated Bylaws of the Company.

               4.3(c)         First Amendment to the Company's Second Amended
                              and Restated Certificate of Incorporation.

               4.4(b)         Specimen Certificate for shares of Common Stock,
                              $.001 par value, of the Company.

               4.5(*)         Amended and Restated Common Stock Purchase
                              Agreement Effective as of November 13, 2000 by and
                              between USinternetworking, Inc. and Acqua
                              Wellington North American Securities Fund, Ltd.

               5.1(#)         Opinion of Latham & Watkins with respect to the
                              validity of the Common Stock.

               23.1(*)        Consent of Ernst & Young LLP, independent auditors
                              (regarding the Company's financial statements).

               23.2(*)        Consent of Bassan & Associados S.C., independent
                              auditors (regarding IIT financial statements).

               23.3(*)        Consent of Ernst & Young LLP, independent auditors
                              (regarding IIT financial statements).

               23.5(#)        Consent of Latham & Watkins (included in Exhibit
                              5.1).

               24.1(#)        Powers of Attorney (included on signature page
                              herein and as previously filed).


*    Filed herewith.

#    Previously filed.

(a)  Incorporated by reference to the Company's Registration Statement on
     Form S-3, as amended (Reg. No. 333-93299).

(b)  Incorporated by reference to the Company's Registration Statement on
     Form S-1, as amended (Reg. No. 333-70717)

(c)  Incorporated by reference to Company's Registration's Statement on
     Form S-1, as amended (Reg. No. 333-95543).






                                       16