-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 TAw+EfSPqmQOaaRGQCbGB9nY2NFxcYdx6I9zU+QD5vjw6OAUepKid+cY/xbDCvb5
 BoqAZf3+zhbE+QoMQaoGrg==

<SEC-DOCUMENT>0001179110-10-005303.txt : 20100315
<SEC-HEADER>0001179110-10-005303.hdr.sgml : 20100315
<ACCEPTANCE-DATETIME>20100315193724
ACCESSION NUMBER:		0001179110-10-005303
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100311
FILED AS OF DATE:		20100315
DATE AS OF CHANGE:		20100315

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			RODRIGUEZ RITA M
		CENTRAL INDEX KEY:			0001195477

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-13459
		FILM NUMBER:		10683386

	MAIL ADDRESS:	
		STREET 1:		3075 ORDWAY STREET NW
		CITY:			WASHINGTON
		STATE:			DC
		ZIP:			20008

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			AFFILIATED MANAGERS GROUP INC
		CENTRAL INDEX KEY:			0001004434
		STANDARD INDUSTRIAL CLASSIFICATION:	INVESTMENT ADVICE [6282]
		IRS NUMBER:				043218510
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		600 HALE STREET
		STREET 2:		/
		CITY:			PRIDES CROSSING
		STATE:			MA
		ZIP:			01965
		BUSINESS PHONE:		6177473300

	MAIL ADDRESS:	
		STREET 1:		600 HALE STREET
		STREET 2:		/
		CITY:			PRIDES CROSSING
		STATE:			MA
		ZIP:			01965
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-03-11</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001004434</issuerCik>
        <issuerName>AFFILIATED MANAGERS GROUP INC</issuerName>
        <issuerTradingSymbol>AMG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001195477</rptOwnerCik>
            <rptOwnerName>RODRIGUEZ RITA M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O AFFILIATED MANAGERS GROUP, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>600 HALE STREET</rptOwnerStreet2>
            <rptOwnerCity>PRIDES CROSSING</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01965</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-03-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5625</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>43.50</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-03-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5625</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>76.43</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Director Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>43.50</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-03-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5625</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>43.50</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2006-12-31</value>
            </exerciseDate>
            <expirationDate>
                <value>2010-07-24</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5625</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The reported amount is the weighted average sales price; the individual transaction prices ranged from $76.15 to $76.55.  Specific transaction details will be provided to the SEC upon request.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ John Kingston, III, Attorney-in-Fact</signatureName>
        <signatureDate>2010-03-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----