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                                                                    EXHIBIT 23.4

               CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS

     We consent to the reference to our firm under the caption "Experts" and to
the use of our report dated February 5, 1999, except for Note 15, as to which
the date is November 8, 1999, with respect to the financial statements of
COMPS.COM, Inc. for the year ended December 31, 1998 in the Registration
Statement (Form S-4) and related Prospectus of CoStar Group, Inc. for the
registration of 2,242,000 shares of its common stock.

     Our audits also included the financial statement schedule of COMPS.COM,
Inc. listed in Item 21(b). This schedule is the responsibility of COMPS.COM
Inc.'s management. Our responsibility is to express an opinion based on our
audits. In our opinion, the financial statement schedule referred to above, when
considered in relation to the basic financial statements taken as a whole,
presents fairly in all material respects the information set forth therein.

                                          /s/ Ernst & Young LLP

San Diego, California
December 8, 1999