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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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<SEC-DOCUMENT>0001104659-10-045900.txt : 20100825
<SEC-HEADER>0001104659-10-045900.hdr.sgml : 20100825
<ACCEPTANCE-DATETIME>20100825165522
ACCESSION NUMBER:		0001104659-10-045900
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100823
FILED AS OF DATE:		20100825
DATE AS OF CHANGE:		20100825

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:		101038197

	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>a4.xml
<DESCRIPTION>4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-08-23</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <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>890 WINTER STREET</rptOwnerStreet1>
            <rptOwnerStreet2>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>2010-08-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>116200</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>20.056</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13013890</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-08-24</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>196800</value>
                    <footnoteId id="F4"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>20.0705</value>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12817090</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F6"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Sale of 114,671 shares of the Issuer's Common Stock by Atlas Venture Fund V, L.P. (&quot;Atlas V&quot;) and of 1,529 shares of the Issuer's Common Stock held 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">Represents a weighted-average price of shares disposed. These shares were sold in multiple transactions at prices ranging from $20.00 to $20.20, inclusive. The reporting person undertakes to provide to the issuer, any security holder of the issuer, or the SEC staff, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth.</footnote>
        <footnote id="F3">Represents aggregate shares beneficially owned after the reported transaction.  Includes 12,842,655 shares held directly by Atlas V and 171,235 shares held directly by 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="F4">Sale of 194,211 shares of the Issuer's Common Stock by Atlas V and of 2,589 shares of the Issuer's Common Stock held 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="F5">Represents a weighted-average price of shares disposed. These shares were sold in multiple transactions at prices ranging from $20.00 to $20.29,inclusive. The reporting person undertakes to provide to the issuer, any security holder of the issuer, or the SEC staff, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth.</footnote>
        <footnote id="F6">Represents aggregate shares beneficially owned after the reported transaction.  Includes 12,648,444 shares held directly by Atlas V and 168,646 shares held directly by 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>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Kristen Laguerre, by power of attorney</signatureName>
        <signatureDate>2010-08-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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