SCHEDULE 14A INFORMATION
           Proxy Statement Pursuant to Section 14(a) of the Securities
                      Exchange Act of 1934 (Amendment No. )

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[ ]  Preliminary Proxy Statement       [ ]  Confidential, for Use of the
                                            Commission Only (as permitted by
                                            Rule 14a-6(e)(2))

[ ]  Definitive Proxy Statement
[X]  Definitive Additional Materials
[ ]  Soliciting Material Pursuant to Section 240.14a-11(c) or Section 240.14a-12


                                   GTSI Corp.
                ------------------------------------------------
                (Name of Registrant as Specified In Its Charter)


    ------------------------------------------------------------------------
    (Name of Person(s) Filing Proxy Statement, if other than the Registrant)


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                                 [LOGO OMITTED]


                                   GTSI CORP.
                            3901 Stonecroft Boulevard
                         Chantilly, Virginia 20151-1010


                    SUPPLEMENT TO GTSI CORP. PROXY STATEMENT
                              Dated March 25, 2004
                                     for the
                       2004 Annual Meeting of Stockholders


To the Stockholders of GTSI Corp.

      This Supplement to the Proxy Statement dated March 25, 2004 of GTSI Corp.,
a Delaware corporation ("GTSI"), is being furnished to stockholders of record as
of the close of business on March 1, 2004, in connection with the solicitation
of proxies by GTSI's board of directors with respect to the annual meeting of
stockholders to be held on Wednesday, April 29, 2004, at 9:00 a.m., local time,
or at any adjournment(s) thereof, for the purposes set forth therein and in the
Notice of Meeting of Stockholders that accompanied such Proxy Statement.

      The Proxy Statement inadvertently misstated on page 19 in the second
sentence of the first full paragraph that the shares of GTSI common stock issued
and issuable under the 1996 Stock Option Plan (the "1996 Plan") totaled
2,500,000. The correct total is 3,500,000 GTSI shares. As of March 1, 2004, (a)
759,359 GTSI shares had been issued pursuant to the exercise of options granted
under the 1996 Plan, (b) 1,600,725 GTSI shares were subject to purchase pursuant
to outstanding options granted under the 1996 Plan and (c) 1,139,916 GTSI shares
remained available for issuance pursuant to future option grants under the 1996
Plan.

      Please read the entire Proxy Statement carefully.


      /s/ John T. Spotila
      --------------------------
      John T. Spotila, Secretary
      March 25, 2004