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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,
 K2kFKb29TPHQ7+aOfqKErwH9iFuK207VUQiMyfseol8oqaHE9KMf2W0DpIEtO3YJ
 K+v2qc+ex+GNIXPhNUEz/Q==

<SEC-DOCUMENT>0001140361-04-000163.txt : 20040106
<SEC-HEADER>0001140361-04-000163.hdr.sgml : 20040106
<ACCEPTANCE-DATETIME>20040106142741
ACCESSION NUMBER:		0001140361-04-000163
CONFORMED SUBMISSION TYPE:	5
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20031231
FILED AS OF DATE:		20040106

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:			TULLY KEVIN P
		CENTRAL INDEX KEY:			0001218865

	FILING VALUES:
		FORM TYPE:		5
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-30739
		FILM NUMBER:		04509451

	BUSINESS ADDRESS:	
		STREET 1:		C/O INSMED INCORPORATED
		STREET 2:		4851 LAKE BROOK DRIVE
		CITY:			GLEN ALLEN
		STATE:			VA
		ZIP:			23060
		BUSINESS PHONE:		804 565 3000

	MAIL ADDRESS:	
		STREET 1:		C/O INSMED INCORP
		STREET 2:		P O BOX 2400
		CITY:			GLEN ALLEN
		STATE:			VA
		ZIP:			23058
</SEC-HEADER>
<DOCUMENT>
<TYPE>5
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 5
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>5</documentType>
<periodOfReport>2003-12-31</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>0001218865</rptOwnerCik>
            <rptOwnerName>TULLY KEVIN P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>4851 LAKE BROOK DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>P.O. BOX 2400</rptOwnerStreet2>
            <rptOwnerCity>GLEN ALLEN</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>23058-2400</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>0</isDirector>
<isOfficer>1</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle>Treasurer, Controller, PFO</officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeTable>
<nonDerivativeHolding>
<securityTitle>
<value>Common Stock</value>
</securityTitle>
<transactionCoding>
<transactionFormType></transactionFormType>
</transactionCoding>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>98024</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, 2003 includes 14,465 shares acquired on June 30, 2003 and 980 shares acquired on December 31, 2003 under the Insmed Incorporated Employee Stock Purchase Plan.</footnote>
</footnotes>
<remarks></remarks>
<ownerSignature>
<signatureName>/s/ Kevin P. Tully, CGA</signatureName>
<signatureDate>2004-01-06</signatureDate>
</ownerSignature>
</ownershipDocument>

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