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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 Eit/C/8Ng2WSJU6hZaq8ddoG7cNR6LUmyu6Zvcsy5uCCpaOdZmVuNTFcU2KpJRkG
 AGpHqUC+0VkIoc3m74/+5Q==

<SEC-DOCUMENT>0001140361-07-003429.txt : 20070214
<SEC-HEADER>0001140361-07-003429.hdr.sgml : 20070214
<ACCEPTANCE-DATETIME>20070214135233
ACCESSION NUMBER:		0001140361-07-003429
CONFORMED SUBMISSION TYPE:	5
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20061231
FILED AS OF DATE:		20070214
DATE AS OF CHANGE:		20070214

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Young Philip J
		CENTRAL INDEX KEY:			0001290682

	FILING VALUES:
		FORM TYPE:		5
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-30739
		FILM NUMBER:		07617794

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		804-565-3000

	MAIL ADDRESS:	
		STREET 1:		C/O INSMED INCORPORATED
		STREET 2:		PO BOX 2400
		CITY:			GLEN ALLEN
		STATE:			VA
		ZIP:			23058

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:			1231

	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>5
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 5
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>5</documentType>

    <periodOfReport>2006-12-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <form3HoldingsReported>0</form3HoldingsReported>

    <form4TransactionsReported>0</form4TransactionsReported>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001290682</rptOwnerCik>
            <rptOwnerName>Young Philip J</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>CBO and EVP, Commercial Ops</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionCoding>
                <transactionFormType></transactionFormType>
            </transactionCoding>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>26732</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The amount of securities beneficially owned at December 31, 2006 includes  5,868 shares acquired on June 30, 2006 under the Amended and Restated Insmed Incorporated 2000 Employee Stock Purchase Plan.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Philip J. Young</signatureName>
        <signatureDate>2007-02-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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