-----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,
 CX5T/6ERsJ2XswvOk84lkD68n8NJAlmb6WoV+yPbOvBDsSLdL9gz3wmoqHFs3sPj
 ShdQBSAFVMBfps/1MjyBcw==

<SEC-DOCUMENT>0001235956-04-000025.txt : 20040527
<SEC-HEADER>0001235956-04-000025.hdr.sgml : 20040527
<ACCEPTANCE-DATETIME>20040527181539
ACCESSION NUMBER:		0001235956-04-000025
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20040526
FILED AS OF DATE:		20040527

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			SANDLER ROBERT MICHAEL
		CENTRAL INDEX KEY:			0001245750

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-10828
		FILM NUMBER:		04836189

	MAIL ADDRESS:	
		STREET 1:		70 PINE ST
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10270

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			21ST CENTURY INSURANCE GROUP
		CENTRAL INDEX KEY:			0000100331
		STANDARD INDUSTRIAL CLASSIFICATION:	FIRE, MARINE & CASUALTY INSURANCE [6331]
		IRS NUMBER:				951935264
		STATE OF INCORPORATION:			CA
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		6301 OWENSMOUTH AVE STE 700
		CITY:			WOODLAND HILLS
		STATE:			CA
		ZIP:			91367
		BUSINESS PHONE:		8187043700

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	20TH CENTURY INDUSTRIES
		DATE OF NAME CHANGE:	19950420
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-05-26</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000100331</issuerCik>
        <issuerName>21ST CENTURY INSURANCE GROUP</issuerName>
        <issuerTradingSymbol>tw</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001245750</rptOwnerCik>
            <rptOwnerName>SANDLER ROBERT MICHAEL</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>6301 OWENSMOUTH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>WOODLAND HILLS</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>91367</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>12.87</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2004-05-26</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>12.87</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2005-05-26</value>
            </exerciseDate>
            <expirationDate>
                <value>2014-05-26</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>36000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <ownerSignature>
        <signatureName>Ronald S. Veltman with Power of Attorney for Robert M. Sandler</signatureName>
        <signatureDate>2004-05-27</signatureDate>
    </ownerSignature>
</ownershipDocument>

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