<SUBMISSION>
<ACCESSION-NUMBER>0001222572-05-000011
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20050203
<FILING-DATE>20050203
<DATE-OF-FILING-DATE-CHANGE>20050203
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>DARBELOFF ALEXANDER V
<CIK>0001222572
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-11859
<FILM-NUMBER>05574094
</FILING-VALUES>
<MAIL-ADDRESS>
<STREET1>C/O PEGASYSTEMS INC
<STREET2>101 MAIN STREET
<CITY>CAMBRIDGE
<STATE>MA
<ZIP>02142
</MAIL-ADDRESS>
</REPORTING-OWNER>
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>PEGASYSTEMS INC
<CIK>0001013857
<ASSIGNED-SIC>7374
<IRS-NUMBER>042787865
<STATE-OF-INCORPORATION>MA
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>101 MAIN ST
<CITY>CAMBRIDGE
<STATE>MA
<ZIP>02142-1590
<PHONE>6173749600
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>101 MAIN ST
<CITY>CAMBRIDGE
<STATE>MA
<ZIP>02142-1590
</MAIL-ADDRESS>
</ISSUER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
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            <rptOwnerStateDescription></rptOwnerStateDescription>
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    </reportingOwner>

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    <ownerSignature>
        <signatureName>Shawn Hoyt, Esq., as Attorney-in-Fact for Alexander V. d'Arbeloff</signatureName>
        <signatureDate>2005-02-03</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
