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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>0001140361-11-005334.txt : 20110201
<SEC-HEADER>0001140361-11-005334.hdr.sgml : 20110201
<ACCEPTANCE-DATETIME>20110201161426
ACCESSION NUMBER:		0001140361-11-005334
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20110131
FILED AS OF DATE:		20110201
DATE AS OF CHANGE:		20110201

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Gurreri Nicholas Lee
		CENTRAL INDEX KEY:			0001507854

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-30739
		FILM NUMBER:		11563333

	MAIL ADDRESS:	
		STREET 1:		PRINCETON CORPORATE PLAZA IV
		STREET 2:		11 DEER PARK DRIVE, SUITE 117
		CITY:			MONMOUTH JUNCTION
		STATE:			NJ
		ZIP:			08852

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			INSMED INC
		CENTRAL INDEX KEY:			0001104506
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		IRS NUMBER:				541972729
		STATE OF INCORPORATION:			VA
		FISCAL YEAR END:			1201

	BUSINESS ADDRESS:	
		STREET 1:		8720 STONY POINT PARKWAY
		STREET 2:		SUITE 200
		CITY:			RICHMOND
		STATE:			VA
		ZIP:			23235
		BUSINESS PHONE:		804-565-3000

	MAIL ADDRESS:	
		STREET 1:		8720 STONY POINT PARKWAY
		STREET 2:		SUITE 200
		CITY:			RICHMOND
		STATE:			VA
		ZIP:			23235
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-01-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001104506</issuerCik>
        <issuerName>INSMED INC</issuerName>
        <issuerTradingSymbol>INSM</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001507854</rptOwnerCik>
            <rptOwnerName>Gurreri Nicholas Lee</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O INSMED INCORPORATED</rptOwnerStreet1>
            <rptOwnerStreet2>8720 STONY POINT PARKWAY, SUITE 200</rptOwnerStreet2>
            <rptOwnerCity>RICHMOND</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>23235</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Senior VP, Commercial Ops</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option - Right to Buy</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.59</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2011-01-31</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>248000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.59</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2012-01-31</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2021-01-31</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>248000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>248000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2011-01-31</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>403000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                    <footnoteId id="F3"/>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>403000</value>
                    <footnoteId id="F3"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>651000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This Option shall be exercisable with respect to twenty-five percent (25%) of the shares of Common Stock subject to this Option on the first anniversary of the Date of Grant and with respect to an additional twelve and a half percent (12.5%) of the shares of Common Stock subject to this Option on the sixth month anniversary of the First Anniversary Date and each sixth month anniversary date thereafter through the fourth anniversary of the Date of Grant.</footnote>
        <footnote id="F2">Pursuant to the Management Agreement these awards are subject to both time (50% of the Award) and performance-based (50% of the Award) vesting. The portion of the Award subject to time-based vesting shall vest on the 3rd anniversary of the grant date or January 31, 2014, so long as the member of management continues to be employed by the Company. The portion of the Award subject to performance-based vesting shall vest based on the date on which the Board determines that Arikace has achieved its primary endpoint in a Phase III trial, provided that the Grantee continues to be employed with the Company on such date.</footnote>
        <footnote id="F3">Restricted Stock Units will be paid to the grantee in cash upon vesting, unless one of the following occurs: 1) the shareholders of the issuer approve an amendment to the issuer's Amended &amp; Restated 2000 Stock Incentive Plan to increase the number of shares of common stock that may be issued under the plan or 2) additional shares become available to the plan through stock option expirations and/or employee terminations, in which case the grantee may receive shares of common stock in lieu of cash.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Nicholas L. Gurreri</signatureName>
        <signatureDate>2011-02-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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