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EXHIBIT 23.1
CONSENT OF INDEPENDENT AUDITORS
We consent to the reference to our firm under the caption "Experts" in Amendment
No. 1 to the Registration Statement (Form S-3 No. 333-39490) and related
prospectus of CoStar Group, Inc. for the registration of 1,123,855 shares of its
common stock and to the incorporation by reference therein of our report dated
March 1, 2000, with respect to the consolidated financial statements of CoStar
Group, Inc. included in its Annual Report (Form 10-K) for the year ended
December 31, 1999, filed with the Securities and Exchange Commission.
/s/ Ernst & Young LLP
McLean, Virginia
August 1, 2000
