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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 6J5yZ0I0XAKAFLISerEc/g==

<SEC-DOCUMENT>0001209191-08-059353.txt : 20081106
<SEC-HEADER>0001209191-08-059353.hdr.sgml : 20081106
<ACCEPTANCE-DATETIME>20081106184714
ACCESSION NUMBER:		0001209191-08-059353
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20081104
FILED AS OF DATE:		20081106
DATE AS OF CHANGE:		20081106

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Isilon Systems, Inc.
		CENTRAL INDEX KEY:			0001373671
		STANDARD INDUSTRIAL CLASSIFICATION:	COMPUTER STORAGE DEVICES [3572]
		IRS NUMBER:				912101027
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		3101 WESTERN AVENUE
		CITY:			SEATTLE
		STATE:			WA
		ZIP:			98121
		BUSINESS PHONE:		206-315-7500

	MAIL ADDRESS:	
		STREET 1:		3101 WESTERN AVENUE
		CITY:			SEATTLE
		STATE:			WA
		ZIP:			98121

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			FIDELMAN BARRY J
		CENTRAL INDEX KEY:			0001030574
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-33196
		FILM NUMBER:		081168428

	BUSINESS ADDRESS:	
		STREET 1:		C/O ATLAS VENTURE
		STREET 2:		222 BERKELEY STREET
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
		BUSINESS PHONE:		781-622-1700

	MAIL ADDRESS:	
		STREET 1:		C/O ATLAS VENTURE
		STREET 2:		890 WINTER STREET, SUITE 320
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02451
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>c76896_4x0.xml
<DESCRIPTION>MAIN DOCUMENT DESCRIPTION
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-11-04</periodOfReport>

    <issuer>
        <issuerCik>0001373671</issuerCik>
        <issuerName>Isilon Systems, Inc.</issuerName>
        <issuerTradingSymbol>ISLN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001030574</rptOwnerCik>
            <rptOwnerName>FIDELMAN BARRY J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ATLAS VENTURE</rptOwnerStreet1>
            <rptOwnerStreet2>890 WINTER STREET, SUITE 320</rptOwnerStreet2>
            <rptOwnerCity>WALTHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02451</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-11-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4085</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>3.4629</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14820971</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-11-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>38722</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>3.3806</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14820971</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Open market purchase of 4,031 shares of the Issuer's Common Stock by Atlas Venture Fund V, L.P (&quot;Atlas V&quot;) and of 54 shares by Atlas Venture Entrepreneurs' Fund V, L.P. (&quot;AVE V&quot;).  These shares are owned directly by Atlas V and AVE V. Barry Fidelman is a Partner of Atlas Venture.  Mr. Fidelman disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein.</footnote>
        <footnote id="F2">Open market purchase of 38,212 shares of the Issuer's Common Stock by Atlas V and of 510 shares by AVE V.  These shares are owned directly by Atlas V and AVE V.  Barry Fidelman is a Partner of Atlas Venture.  Mr. Fidelman disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein.</footnote>
        <footnote id="F3">Represents aggregate shares beneficially owned after all of the reported transactions. Includes 14,625,959 shares held directly by Atlas V (including 2,902,082 previously reported as held directly by Atlas Venture Parallel Fund V-A, C.V.) and 195,012 shares held directly by AVE V. Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Jeanne Larkin Henry - Attorney in Fact</signatureName>
        <signatureDate>2008-11-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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