<ARTICLE> 5
<LEGEND>
This schedule contains summary financial information extracted from the
condensed consolidated balance sheet and statement of operations of COSTAR
GROUP, INC. as of and for the six months ended June 30, 1999 and is qualified in
its entirety by reference to such financial statements.
</LEGEND>

                             
<PERIOD-TYPE>                   OTHER
<FISCAL-YEAR-END>                          DEC-31-1999
<PERIOD-END>                               JUN-30-1999
<CASH>                                     102,424,000
<SECURITIES>                                         0
<RECEIVABLES>                                2,753,000
<ALLOWANCES>                                   600,000
<INVENTORY>                                          0
<CURRENT-ASSETS>                           105,064,000
<PP&E>                                       5,792,000
<DEPRECIATION>                               1,708,000
<TOTAL-ASSETS>                             132,997,000
<CURRENT-LIABILITIES>                        7,668,000
<BONDS>                                              0
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                       128,000
<OTHER-SE>                                 125,201,000
<TOTAL-LIABILITY-AND-EQUITY>               132,997,000
<SALES>                                              0
<TOTAL-REVENUES>                            13,305,000
<CGS>                                                0
<TOTAL-COSTS>                                5,662,000
<OTHER-EXPENSES>                            13,111,000
<LOSS-PROVISION>                               274,000
<INTEREST-EXPENSE>                                   0
<INCOME-PRETAX>                            (5,468,000)
<INCOME-TAX>                                         0
<INCOME-CONTINUING>                        (4,790,000)
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                               (4,790,000)
<EPS-BASIC>                                     (0.45)
<EPS-DILUTED>                                   (0.45)