<SUBMISSION>
<ACCESSION-NUMBER>0001057352-07-000006
<TYPE>8-K
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20070222
<ITEMS>1.01
<FILING-DATE>20070227
<DATE-OF-FILING-DATE-CHANGE>20070227
<FILER>
<COMPANY-DATA>
<CONFORMED-NAME>COSTAR GROUP INC
<CIK>0001057352
<ASSIGNED-SIC>7389
<IRS-NUMBER>522091509
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<FILING-VALUES>
<FORM-TYPE>8-K
<ACT>34
<FILE-NUMBER>000-24531
<FILM-NUMBER>07653748
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>2 BETHESDA METRO CENTER
<STREET2>10TH FLOOR
<CITY>BETHESDA
<STATE>MD
<ZIP>20814
<PHONE>3012158300
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>2 BETHESDA METRO CENTER
<STREET2>10TH FLOOR
<CITY>BETHESDA
<STATE>MD
<ZIP>20814
</MAIL-ADDRESS>
</FILER>
<DOCUMENT>
<TYPE>8-K
<SEQUENCE>1
<FILENAME>form8-k.htm
<DESCRIPTION>CURRENT REPORT, ITEM 1.01
<TEXT>
<html>
  <head>
    <title>
      Current Report, Item 1.01
</title>
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      STATES</strong></font></div>
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      AND EXCHANGE COMMISSION</strong></font></div>
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      8-K</strong></font></div>
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    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 0pt; LINE-HEIGHT: 1.25; MARGIN-RIGHT: 0pt" align="center"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman"><strong>CURRENT
      REPORT</strong></font></div>
    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 0pt; LINE-HEIGHT: 1.25; MARGIN-RIGHT: 0pt" align="center"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman"><strong>Pursuant
      to Section 13 or 15(d) of the Securities Exchange Act of
      1934</strong></font></div>
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      of
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      the
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      satisfy the filing obligation of the registrant under any of the following
      provisions (see General Instruction A.2. below):</font></div>
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      Written communications pursuant to Rule 425 under the Securities Act (17 CFR
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      Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR
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      Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange
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      Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange
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    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 0pt; LINE-HEIGHT: 1.25; MARGIN-RIGHT: 0pt" align="justify">&#160;</div><br>
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      <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 0pt; LINE-HEIGHT: 1.25; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman"><strong>Item
        1.01. Entry into a Material Definitive Agreement</strong></font></div>
      <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 0pt; LINE-HEIGHT: 1.25; MARGIN-RIGHT: 0pt" align="left"><br></div>
      <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 0pt; LINE-HEIGHT: 1.25; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman">Effective
        as of February 22, 2007, CoStar Realty Information, Inc. (&#8220;CoStar&#8221;) and Gateway,
        Inc. (&#8220;Gateway&#8221;) executed an amendment (the &#8220;Amendment&#8221;) to a sublease agreement
        (the &#8220;Sublease&#8221;), pursuant to which CoStar has exercised its option to extend
        the Sublease for an additional five-year term commencing September 1, 2007
        and
        expiring August 31, 2012. Under the Sublease, CoStar leases from Gateway
        approximately 41,551 square feet of office space located within the building
        known as 4535 Towne Centre Court, San Diego, CA 92121. The Amendment extending
        the Sublease has an average base rent of approximately $26.76 per rentable
        square foot per year (excluding property tax and service charges).
</font></div><br></div>
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    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 0pt; LINE-HEIGHT: 1.25; MARGIN-RIGHT: 0pt" align="justify">&#160;</div>
    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 27pt; LINE-HEIGHT: 1.25; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman">Pursuant
      to the requirements of the Securities Exchange Act of 1934, the registrant
      has
      duly caused this report to be signed on its behalf by the undersigned hereunto
      duly authorized.</font></div>
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                GROUP, INC.</font></div>
            </td>
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            <td align="left" valign="top" width="45%">&#160;</td>
            <td valign="top" width="45%">&#160;</td>
          </tr>
          <tr>
            <td align="left" valign="top" width="45%">&#160;</td>
            <td align="left" valign="top" width="45%">
              <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 0pt; LINE-HEIGHT: 1.25; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman">By:
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                February 27, 2007</font></div>
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                Frank&#160;A.
                Carchedi&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;
                </u></font><font id="TAB2" style="COLOR: black; LETTER-SPACING: 27pt">&#160;</font><font id="TAB2" style="COLOR: black; LETTER-SPACING: 27pt">&#160;</font><font id="TAB2" style="COLOR: black; LETTER-SPACING: 27pt">&#160;</font></div>
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            <td valign="top" width="45%">&#160;</td>
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            <td align="left" valign="top" width="45%">
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                Frank A. Carchedi</font></div>
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                Chief Financial Officer</font></div>
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