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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 O0LXZoOtGxGLOL9dxG24emJYu9qPVPFW2eHKiYamZirieki1d0NVeq8M/p2uzC6j
 eUVhO6WuRpTbGJtYC+nKIQ==

<SEC-DOCUMENT>0001140361-04-003100.txt : 20040517
<SEC-HEADER>0001140361-04-003100.hdr.sgml : 20040517
<ACCEPTANCE-DATETIME>20040517163408
ACCESSION NUMBER:		0001140361-04-003100
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20040505
FILED AS OF DATE:		20040517

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:		800 E LEIGH ST
		STREET 2:		SUITE 206
		CITY:			RICHMOND
		STATE:			VA
		ZIP:			23219
		BUSINESS PHONE:		8088286893

REPORTING-OWNER:	

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

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-30739
		FILM NUMBER:		04812923

	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
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 3
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2004-05-05</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <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>4851 LAKE BROOK DRIVE</rptOwnerStreet2>
            <rptOwnerCity>GLEN ALLEN</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>23060</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Bus. Offcr, EVP Comm Ops</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>3.00</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2010-04-07</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>150000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">One-fourth of the shares of Common Stock subject to this Option will vest and become exercisable on April 7th of each year commencing on April 7, 2005 with all shares fully vested on April 7, 2008.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Kevin P. Tully, as attorney-in-fact</signatureName>
        <signatureDate>2004-05-17</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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