##### Table of Contents



UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
 Washington, D.C. 20549
 FORM 10-K
 ANNUAL REPORT
PURSUANT TO SECTIONS 13 OR 15(d)
OF THE SECURITIES EXCHANGE ACT OF 1934
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    ANNUAL REPORT PURSUANT TO SECTION 13 OR
15(d) OF THE SECURITIES EXCHANGE ACT OF
1934
 For the fiscal year ended December 31, 2005
 OR
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    TRANSITION REPORT PURSUANT TO SECTION 13
OR 15(d) OF THE SECURITIES EXCHANGE ACT
OF 1934
 For
the transition period
from                    
to
 Commission
file number
333-110499-124
 Principal Life Income Fundings Trust 2005-31
 (by Principal Life Insurance Company as depositor)
  Iowa
(State or other jurisdiction of
incorporation or organization)
    
    42-0127290
(I.R.S. Employer Identification No.)
 Principal Life Income Fundings Trust 2005-31
c/o Principal Life Insurance Company, as depositor
711 High Street
Des Moines, Iowa 50392-0001
(515) 247-5111
 (515) 247-5111
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TABLE OF CONTENTS  PART IItem 3. Legal ProceedingsItem 4. Submission of Matters to a Vote of Security HoldersPART IIItem 5. Market for Registrants Common Equity, Related Stockholder Matters and Issuer Purchases of Equity SecuritiesPART IIIItem 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder MattersItem 13. Certain Relationships and Related TransactionsPART IVItem 15. Exhibits, Financial Statement Schedules, and Reports on Form 8-KSIGNATURESEXHIBIT INDEXCertificationAnnual Statement of ComplianceReport of Independent Registered Public Accounting Firm    Table of Contents  
 PART I
 
 Item 3. Legal Proceedings.
  
 Item 4. Submission of Matters to a Vote of Security Holders.
  
 PART II
 
 Item 5. Market for Registrants Common Equity, Related Stockholder Matters and Issuer Purchases of
Equity Securities.
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##### Table of Contents



PART III
 
 Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder
Matters.
  
 Item 13. Certain Relationships and Related Transactions.
  
 PART IV
 
 Item 15. Exhibits, Financial Statement Schedules, and Reports on Form 8-K.
 Exhibit 31.1
    
    Section 302 Certification.Exhibit 99.1
    
    Indenture Trustee Reports of the Trust  Incorporated herein by
reference to Exhibit 99.1 to the Current Report(s) on Form 8-K filed
by Principal Life Insurance Company on behalf of Principal Life
Income Fundings Trust 2005-31 on October 24, 2005.Exhibit 99.2
    
    Annual Statement of Compliance by Citibank, N.A.Exhibit 99.3
    
    Report of Independent Registered Public Accounting Firm on Compliance.
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##### Table of Contents



SIGNATURES
  PRINCIPAL LIFE INSURANCE COMPANY
(Registrant)Date: March 24, 2006
    By:
    /s/ Karen A. PearstonName:
    Karen A. PearstonTitle:
    Second Vice President and Counsel 4




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##### Table of Contents



EXHIBIT INDEX
 ExhibitNumber
    
    DescriptionExhibit 31.1
    
    Section 302 Certification.Exhibit 99.1
    
    Indenture Trustee Reports of the Trust  Incorporated herein by
reference to Exhibit 99.1 to the Current Report(s) on Form 8-K filed
by Principal Life Insurance Company on behalf of Principal Life
Income Fundings Trust 2005-31 on October 24, 2005.Exhibit 99.2
    
    Annual Statement of Compliance by Citibank, N.A.Exhibit 99.3
    
    Report of Independent Registered Public Accounting Firm on Compliance.
 5