-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
 MFgwCgYEVQgBAQICAf8DSgAwRwJAW2sNKK9AVtBzYZmr6aGjlWyK3XmZv3dTINen
 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 I8FL/sA4vafmCOo4zlAbK6rRepYZauqIExw7+gMj1OALsCLbb7foG+5AuD7mjsDr
 PCIgObEVQnoXXbS3GVYhug==

<SEC-DOCUMENT>0001179110-04-018907.txt : 20040929
<SEC-HEADER>0001179110-04-018907.hdr.sgml : 20040929
<ACCEPTANCE-DATETIME>20040929113013
ACCESSION NUMBER:		0001179110-04-018907
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20040927
FILED AS OF DATE:		20040929
DATE AS OF CHANGE:		20040929

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			OBRIEN EDWARD C
		CENTRAL INDEX KEY:			0001282922

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-32033
		FILM NUMBER:		041051625

	MAIL ADDRESS:	
		STREET 1:		11480 COMMERCE PARK DR
		STREET 2:		STE 600
		CITY:			RESTON
		STATE:			VA
		ZIP:			20191

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			TNS INC
		CENTRAL INDEX KEY:			0001268671
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-BUSINESS SERVICES, NEC [7389]
		IRS NUMBER:				364430020

	BUSINESS ADDRESS:	
		STREET 1:		11480 COMMERCE PARK DR.
		STREET 2:		SUITE 600
		CITY:			RESTON
		STATE:			VA
		ZIP:			20191-1406
		BUSINESS PHONE:		7034538300

	MAIL ADDRESS:	
		STREET 1:		11480 COMMERCE PARK DR.
		STREET 2:		SUITE 600
		CITY:			RESTON
		STATE:			VA
		ZIP:			20191-1406
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-09-27</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001268671</issuerCik>
        <issuerName>TNS INC</issuerName>
        <issuerTradingSymbol>TNS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001282922</rptOwnerCik>
            <rptOwnerName>OBRIEN EDWARD C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>11480 COMMERCE PARK DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE #600</rptOwnerStreet2>
            <rptOwnerCity>RESTON</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>20191</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP, Corp. Controller</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-09-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>24389</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>20.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>110512</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>/s/ Michael Keegan, pursuant to power of attorney previously filed</signatureName>
        <signatureDate>2004-09-29</signatureDate>
    </ownerSignature>
</ownershipDocument>

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