UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13D
                                 (Rule 13d-101)

                                (Amendment No. 16)

    INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULE 13d-1(a)
                    AND AMENDMENTS THERETO FILED PURSUANT TO
                                  RULE 13d-2(a)

                            Prime Group Realty Trust
--------------------------------------------------------------------------------
                                (Name of Issuer)

                      Common Shares of Beneficial Interest,
                            par value $0.01 per share
                            -------------------------
                         (Title of Class of Securities)

                                    74158J103
                                    ---------
                                 (CUSIP Number)

                                  Joseph Macnow
                              Vornado Realty Trust
                               888 Seventh Avenue
                            New York, New York 10019
                                 (212) 894-7000
--------------------------------------------------------------------------------
            (Name, Address and Telephone Number of Person Authorized
                     to Receive Notices and Communications)

                                 With a copy to:
                                William G. Farrar
                                 Alan Sinsheimer
                               Sullivan & Cromwell
                                125 Broad Street
                            New York, New York 10004
                                 (212) 558-4000

                                  May 23, 2003
          --------------------------------------------------------------
             (Date of Event Which Requires Filing of This Statement)

If a filing person has previously filed a statement on Schedule 13G to report
the acquisition that is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box
[ ].

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities
of that section of the Exchange Act but shall be subject to all other provisions
of the Exchange Act.

                         (Continued on following pages)
                               (Page 1 of 7 Pages)

--------------------                                       ---------------------
CUSIP NO. 74158J103                                            PAGE 2 OF 7 PAGES
--------------------                                       ---------------------
--------------------------------------------------------------------------------
 1.   NAME OF REPORTING PERSON: Vornado Realty Trust
      I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):
      22-1657560
--------------------------------------------------------------------------------
 2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
                                                                     (a)  [X]
                                                                     (b)  [ ]
--------------------------------------------------------------------------------
 3.   SEC USE ONLY

--------------------------------------------------------------------------------
 4.   SOURCE OF FUNDS:
      AF

--------------------------------------------------------------------------------
 5.   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS
      REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)                             [ ]
--------------------------------------------------------------------------------
 6.   CITIZENSHIP OR PLACE OF ORGANIZATION
      Maryland
--------------------------------------------------------------------------------
               7.   SOLE VOTING POWER
  NUMBER OF         0
   SHARES      -----------------------------------------------------------------
BENEFICIALLY   8.   SHARED VOTING POWER
  OWNED BY          3,972,447
    EACH       -----------------------------------------------------------------
 REPORTING     9.   SOLE DISPOSITIVE POWER
   PERSON           0
    WITH       -----------------------------------------------------------------
               10.  SHARED DISPOSITIVE POWER
                    7,944,893
--------------------------------------------------------------------------------
11.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING
      PERSON
      7,944,893
--------------------------------------------------------------------------------
12.   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES
      CERTAIN SHARES                                                      [ ]
--------------------------------------------------------------------------------
13.   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
      33.6% as calculated in accordance with Rule 13d-3(d)(1)
--------------------------------------------------------------------------------
14.   TYPE OF REPORTING PERSON
      OO (real estate investment trust)
--------------------------------------------------------------------------------


                                       -2-

--------------------                                       ---------------------
CUSIP NO. 74158J103                                            PAGE 3 OF 7 PAGES
--------------------                                       ---------------------
--------------------------------------------------------------------------------
 1.   NAME OF REPORTING PERSON: Vornado Realty L.P.
      I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):
      13-3925979
--------------------------------------------------------------------------------
 2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
                                                                     (a)  [X]
                                                                     (b)  [ ]
--------------------------------------------------------------------------------
 3.   SEC USE ONLY

--------------------------------------------------------------------------------
 4.   SOURCE OF FUNDS
      WC

--------------------------------------------------------------------------------
 5.   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS
      REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)                             [ ]
--------------------------------------------------------------------------------
 6.   CITIZENSHIP OR PLACE OF ORGANIZATION
      Delaware
--------------------------------------------------------------------------------
               7.   SOLE VOTING POWER
  NUMBER OF         0
   SHARES      -----------------------------------------------------------------
BENEFICIALLY   8.   SHARED VOTING POWER
  OWNED BY          3,972,447
    EACH       -----------------------------------------------------------------
 REPORTING     9.   SOLE DISPOSITIVE POWER
   PERSON           0
    WITH       -----------------------------------------------------------------
               10.  SHARED DISPOSITIVE POWER
                    7,944,893
--------------------------------------------------------------------------------
11.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING
      PERSON
      7,944,893
--------------------------------------------------------------------------------
12.   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES
      CERTAIN SHARES                                                      [ ]
--------------------------------------------------------------------------------
13.   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
      33.6% as calculated in accordance with Rule 13d-3(d)(1)
--------------------------------------------------------------------------------
14.   TYPE OF REPORTING PERSON
      PN
--------------------------------------------------------------------------------


                                       -3-

--------------------                                       ---------------------
CUSIP NO. 74158J103                                            PAGE 4 OF 7 PAGES
--------------------                                       ---------------------
--------------------------------------------------------------------------------
 1.   NAME OF REPORTING PERSON: Vornado PS, L.L.C.
      I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY):
--------------------------------------------------------------------------------
 2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
                                                                     (a)  [X]
                                                                     (b)  [ ]
--------------------------------------------------------------------------------
 3.   SEC USE ONLY

--------------------------------------------------------------------------------
 4.   SOURCE OF FUNDS:
      AF
--------------------------------------------------------------------------------
 5.   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS
      REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)                             [ ]
--------------------------------------------------------------------------------
 6.   CITIZENSHIP OR PLACE OF ORGANIZATION
      Delaware
--------------------------------------------------------------------------------
               7.   SOLE VOTING POWER
  NUMBER OF         0
   SHARES      -----------------------------------------------------------------
BENEFICIALLY   8.   SHARED VOTING POWER
  OWNED BY          3,972,447
    EACH       -----------------------------------------------------------------
 REPORTING     9.   SOLE DISPOSITIVE POWER
   PERSON           0
    WITH       -----------------------------------------------------------------
               10.  SHARED DISPOSITIVE POWER
                    7,944,893
--------------------------------------------------------------------------------
11.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING
      PERSON
      7,944,893
--------------------------------------------------------------------------------
12.   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES
      CERTAIN SHARES                                                      [ ]
--------------------------------------------------------------------------------
13.   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
      33.6% as calculated in accordance with Rule 13d-3(d)(1)
--------------------------------------------------------------------------------
14.   TYPE OF REPORTING PERSON
      OO (limited liability company)
--------------------------------------------------------------------------------


                                       -4-

                         AMENDMENT NO. 16 TO SCHEDULE 13D
             RELATING TO THE COMMON SHARES OF BENEFICIAL INTEREST OF
                            PRIME GROUP REALTY TRUST

         Vornado Realty Trust ("Vornado"), Vornado Realty L.P. (the "Operating
Partnership") and Vornado PS, L.L.C. ("Vornado PS" and, collectively with
Vornado and the Operating Partnership, the "Reporting Persons") hereby amend
their Statement on Schedule 13D filed with respect to the Common Shares of
Beneficial Interest, par value $0.01 per share ("Common Shares"), of Prime Group
Realty Trust, a Maryland real estate investment trust (the "Issuer"). This
Amendment No. 16 to Schedule 13D ("Amendment No. 16") should be read in
conjunction with the Statement on Schedule 13D of the Reporting Persons filed on
November 2, 2001 (the "Initial Schedule 13D"), as amended by Amendment No. 1 to
Schedule 13D of the Reporting Persons filed on November 20, 2001, by Amendment
No. 2 to Schedule 13D of the Reporting Persons filed on December 19, 2001, by
Amendment No. 3 to Schedule 13D of the Reporting Persons filed on December 21,
2001, by Amendment No. 4 to Schedule 13D of the Reporting Persons filed on
December 27, 2001, by Amendment No. 5 to Schedule 13D of the Reporting Persons
filed on January 15, 2002, by Amendment No. 6 to Schedule 13D of the Reporting
Persons filed on January 31, 2002, by Amendment No. 7 to Schedule 13D of the
Reporting Persons filed on February 7, 2002, by Amendment No. 8 to Schedule 13D
of the Reporting Persons filed on February 20, 2002, by Amendment No. 9 to
Schedule 13D of the Reporting Persons filed on March 29, 2002, by Amendment No.
10 to Schedule 13D of the Reporting Persons filed on April 17, 2002, by
Amendment No. 11 to Schedule 13D of the Reporting Persons filed on April 19,
2002, by Amendment No. 12 to Schedule 13D of the Reporting Persons filed on May
1, 2002, by Amendment No. 13 to Schedule 13D of the Reporting Persons filed on
May 14, 2002, by Amendment No. 14 to Schedule 13D of the Reporting Persons filed
on June 28, 2002 and by Amendment No. 15 to Schedule 13D of the Reporting
Persons filed on December 23, 2002 (as so amended, the "Schedule 13D"). This
Amendment No. 16 amends the Schedule 13D only with respect to the items listed
below. Unless otherwise indicated, all capitalized terms used but not defined
herein shall have the meaning ascribed to them in the Initial Schedule 13D.

         Pursuant to Rule 13d-4 under the Exchange Act, each of the Reporting
Persons declares that the filing of this statement shall not be construed as an
admission that such Reporting Person is, for the purposes of Section 13(d) or
13(g) of the Exchange Act, the beneficial owner of any Common Shares.

         Any disclosures made herein with respect to persons other than the
Reporting Persons are made on information and belief after making appropriate
inquiry.

Item 4.  Purpose of the Transaction.

Item 4 is hereby amended by adding the following paragraphs at the end thereof:

         On May 23, 2003, pursuant to the terms of the Agreement of Limited
Partnership of Prime Group Realty, L.P., dated November 17, 1997 (the "Prime
Group Realty, L.P. Partnership Agreement") and the terms of the Consent and
Agreement, dated September 26, 2000, by the Issuer and Prime Group Realty, L.P.,
in favor or Vornado PS, which has been filed as Exhibit 99.7 to this Schedule
13D (the "Consent and Agreement"), Vornado PS delivered to the Issuer an
Exchange Exercise Notice electing to

                                      -5-

exercise its Exchange Rights (as defined in the Prime Group Realty, L.P.
Partnership Agreement) with regard to all of the 3,972,447 Common Units it
purchased at a foreclosure auction held on April 30, 2002. In accordance with
the terms of the Prime Group Realty, L.P. Partnership Agreement and the Consent
and Agreement, the Issuer must, by June 5, 2003, elect to deliver either Common
Shares (one Common Share for each Common Unit) or the Cash Purchase Price (as
defined in the Prime Group Realty, L.P. Partnership Agreement) to Vornado PS in
exchange for its Common Units. The Cash Purchase Price, calculated in
accordance with the Prime Group Realty, L.P. Partnership Agreement, is $6.72
per Common Unit. As of the date hereof, Vornado PS has not been notified as to
whether it will receive Common Shares or the Cash Purchase Price.

     On May 23, 2003, Cadim Acquisition also delivered to the Issuer an Exchange
Exercise Notice electing to exercise its Exchange Rights with regard to all of
the 3,972,446 Common Units it holds.

Item 5.  Interest in Securities of the Issuer.

Item 5 is hereby amended by adding the following sentence at the end of
paragraph (c) thereof:

     No transactions in the Common Shares were effected by Reporting Persons
since December 23, 2002, except to the extent that such transactions may be
deemed to have occurred as described in Item 4.


                                     -6-

                                   SIGNATURES

         After reasonable inquiry and to the best of my knowledge and belief,
each of the undersigned certifies that the information set forth in this
amendment to Schedule 13D is true, complete and correct.
Dated: May 27, 2003
                                  VORNADO REALTY TRUST


                                  By:  /s/  Joseph Macnow
                                     ---------------------------------------
                                     Name:  Joseph Macnow
                                     Title: Executive Vice
                                            President-Finance
                                            and Administration,
                                            Chief Financial Officer

                                  VORNADO REALTY L.P.

                                  By: VORNADO REALTY TRUST,
                                      its general partner


                                  By:  /s/  Joseph Macnow
                                      ---------------------------------------
                                      Name:  Joseph Macnow
                                      Title: Executive Vice
                                             President-Finance
                                             and Administration,
                                             Chief Financial Officer


                                  VORNADO PS, L.L.C.

                                  By: VORNADO REALTY L.P.,
                                      its sole member

                                  By: VORNADO REALTY TRUST,
                                      its general partner


                                  By:  /s/  Joseph Macnow
                                     ---------------------------------------
                                     Name:  Joseph Macnow
                                     Title: Executive Vice
                                            President-Finance
                                            and Administration,
                                            Chief Financial Officer


                                      -7-