UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-K

Commission File Number 0-20006

ANCHOR BANCORP WISCONSIN INC.

(Exact name of registrant as specified in its charter)

25 West Main Street

Madison, Wisconsin 53703

(Address of principal executive office)

Registrant’s telephone number, including area code (608) 252-8700

Securities registered pursuant to Section 12 (b) of the Act

Common stock, par value $.10 per share

Preferred Stock Purchase Rights

(Title of Class)

Securities registered pursuant to Section 12 (g) of the Act:

Not Applicable

      Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.     Yes o          No þ

      Indicate by check mark if the registrant is a not required to file reports pursuant to Section 13 or Section 15(d) of the Act.     Yes o          No þ

      Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports) and (2) has been subject to such filing requirements for the past 90 days.     Yes þ          No o

      Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 or Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of the Form 10-K or any amendment to this Form 10-K.     o

      Indicate by check mark whether the Registrant is a large accelerated filer, an accelerated filer, or a non-accelerated filer. See definition of “accelerated filer” in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated filer o          Accelerated filer þ          Non-accelerated filer o

      Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act).     Yes o          No þ

      As of September 30, 2005, the aggregate market value of the 22,080,494 outstanding shares of the registrant’s common stock deemed to be held by non-affiliates of the registrant was $571.2 million, based upon the closing price of $29.48 per share of common stock as reported by the Nasdaq Stock Market, National Market System on such date. Although directors and executive officers of the registrant and certain of its employee benefit plans were assumed to be “affiliates” of the registrant for purposes of this calculation, the classification is not to be interpreted as an admission of such status.

      As of June 9, 2006, 21,937,991 shares of the registrant’s common stock were outstanding. There were also 100,000 Series A- preferred stock purchase rights authorized with none outstanding as of the same date.

DOCUMENTS INCORPORATED BY REFERENCE

      Portions of the definitive Proxy Statement for the Annual Meeting of Stockholders to be held on July 25, 2006 (Part III, Items 10 to 14).

ANCHOR BANCORP WISCONSIN INC.

FISCAL 2006 FORM 10-K ANNUAL REPORT

TABLE OF CONTENTS

FORWARD-LOOKING STATEMENTS

      In the normal course of business, we, in an effort to help keep our shareholders and the public informed about our operations, may from time to time issue or make certain statements, either in writing or orally, that are or contain forward-looking statements, as that term is defined in the U.S. federal securities laws. Generally, these statements relate to business plans or strategies, projected or anticipated benefits from acquisitions made by or to be made by us, projections involving anticipated revenues, earnings, profitability or other aspects of operating results or other future developments in our affairs or the industry in which we conduct business. Forward-looking statements may be identified by reference to a future period or periods or by the use of forward-looking terminology such as “anticipate,” “believe,” “expect,” “intend,” “plan,” “estimate” or similar expressions.

      Although we believe that the anticipated results or other expectations reflected in our forward-looking statements are based on reasonable assumptions, we can give no assurance that those results or expectations will be attained. Forward-looking statements involve risks, uncertainties and assumptions (some of which are beyond our control), and as a result actual results may differ materially from those expressed in forward-looking statements. Factors that could cause actual results to differ from forward-looking statements include, but are not limited to, the following, as well as those discussed elsewhere herein:

      You should not put undue reliance on any forward-looking statements. Forward-looking statements speak only as of the date they are made, and we undertake no obligation to update them in light of new information or future events except to the extent required by federal securities laws.

PART I

General

      We, Anchor BanCorp Wisconsin Inc. (the “Corporation” or the “Company”) are a registered savings and loan holding company incorporated under the laws of the State of Wisconsin and are engaged in the savings and loan business through its wholly-owned banking subsidiary, AnchorBank, fsb (the “Bank”).

      The Bank was organized in 1919 as a Wisconsin-chartered savings institution and converted to a federally-chartered savings institution in July 2000. The Bank’s deposits are insured up to the maximum allowable amount by the Federal Deposit Insurance Corporation (“FDIC”). The Bank is a member of the Federal Home Loan Bank (“FHLB”) of Chicago, and is regulated by the Office of Thrift Supervision (“OTS”) and the FDIC. The Corporation is regulated by the OTS as a savings and loan holding company and is subject to the periodic reporting requirements of the Securities and Exchange Commission (“SEC”) under the Securities Exchange Act of 1934, as amended (“Exchange Act”). See “Regulation and Supervision.”

      The Bank blends an interest in the consumer and small business markets with the willingness to expand its numerous checking, savings and lending programs to meet customers’ changing financial needs. The Bank offers checking, savings, money market accounts, mortgages, home equity and other consumer loans, student loans, credit cards, annuities and related consumer financial services. The Bank also offers banking services to businesses, including checking accounts, lines of credit, secured loans and commercial real estate loans.

      The Corporation has a non-banking subsidiary, Investment Directions, Inc. (“IDI”), a Wisconsin corporation which invests in real estate partnerships. IDI has two subsidiaries, Nevada Investment Directions, Inc. (“NIDI”) and California Investment Directions, Inc. (“CIDI”), both of which invest in real estate held for development and sale.

      The Bank has three wholly-owned subsidiaries: Anchor Investment Services, Inc. (“AIS”), a Wisconsin corporation, offers investments and credit life and disability insurance to the Bank’s customers and other members of the general public; ADPC Corporation (“ADPC”), a Wisconsin corporation, holds and develops certain of the Bank’s foreclosed properties; and Anchor Investment Corporation (“AIC”) is an operating subsidiary that is located in and formed under the laws of the State of Nevada. AIC was formed for the purpose of managing a portion of the Bank’s investment portfolio (primarily mortgage-related securities).

      The Corporation maintains a web site at www.anchorbank.com. All the Corporation’s filings under the Exchange Act are available through that web site, free of charge, including copies of Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and amendments to those reports, on the date that the Corporation files those materials with, or furnishes them to, the SEC.

Market Area

      The Bank’s primary market area consists of the metropolitan area of Madison, Wisconsin, the suburban communities of Dane County, Wisconsin, south-central Wisconsin, the Fox Valley in east-central Wisconsin, the Milwaukee metropolitan area in southeastern Wisconsin, as well as contiguous counties in Iowa, Minnesota, and Illinois. At March 31, 2006, the Bank conducted business from its headquarters and main office in Madison, Wisconsin and from 58 other full-service offices and two loan origination offices.

Competition

      The Bank encounters strong competition in attracting both loan and deposit customers. Such competition includes banks, savings institutions, mortgage banking companies, credit unions, finance companies, mutual funds, insurance companies and brokerage and investment banking firms. The Bank’s market area includes branches of several commercial banks that are substantially larger in terms of loans and deposits. Furthermore, tax exempt credit unions operate in most of the Bank’s market area and aggressively price their products and

services to a large portion of the market. The Corporation’s profitability depends upon the Bank’s continued ability to successfully maintain and increase market share.

      The origination of loans secured by real estate is the Bank’s primary business and principal source of profits. If customer demand for real estate loans decreases, the Bank’s income could be affected because alternative investments, such as securities, typically earn less income than real estate secured loans. Customer demand for loans secured by real estate could be reduced by a weaker economy, an increase in unemployment, a decrease in real estate values, or an increase in interest rates.

      The principal factors that are used to attract deposit accounts and that distinguish one financial institution from another include rates of return, types of accounts, service fees, convenience of office locations and hours, and other services. The primary factors in competing for loans are interest rates, loan fee charges, timeliness and quality of service to the borrower.

Lending Activities

      General. At March 31, 2006, the Bank’s net loans held for investment totaled $3.61 billion, representing approximately 84.5% of its $4.28 billion of total assets at that date. Approximately $3.0 billion, or 78.4%, of the Bank’s total loans held for investment at March 31, 2006 were secured by first liens on real estate.

      The Bank originates single-family residential loans secured by properties located primarily in Wisconsin, with adjustable-rate loans generally being originated for inclusion in the Bank’s loan portfolio and fixed-rate loans generally being originated for sale into the secondary market. In order to increase the yield and interest rate sensitivity of its portfolio, the Bank also emphasizes the origination of commercial real estate, multi-family, construction, consumer and commercial business loans secured by properties and assets located primarily in its primary market area.

      Non-real estate loans originated by the Bank consist of a variety of consumer loans and commercial business loans. At March 31, 2006, the Bank’s total loans held for investment included $622.3 million, or 16.3%, of consumer loans and $205.0 million, or 5.4%, of commercial business loans.

      Loan Portfolio Composition. The following table presents information concerning the composition of the Bank’s consolidated loans held for investment at the dates indicated.

      The following table shows, at March 31, 2006, the scheduled contractual maturities of the Bank’s consolidated gross loans held for investment, as well as the dollar amount of such loans which are scheduled to mature after one year which have fixed or adjustable interest rates.

      Single-Family Residential Loans. At March 31, 2006, $785.4 million, or 20.5%, of the Bank’s total loans held for investment consisted of single-family residential loans, substantially all of which are conventional loans, which are neither insured nor guaranteed by a federal or state agency. Although the Bank continues to originate single-family residential loans, they have declined as a percentage of the Bank’s total loans held for investment from 30.2% at March 31, 2002 to 20.5% at March 31, 2006.

      The adjustable-rate loans currently emphasized by the Bank have up to 30-year maturities and terms which permit the Bank to annually increase or decrease the rate on the loans, based on a designated index. This is generally subject to a limit of 2% per adjustment and an aggregate 6% adjustment over the life of the loan. The Bank makes a limited number of interest-only loans and does not make payment option loans, pursuant to which a consumer may select a payment option which can result in negative amortization on the loan.

      Adjustable-rate loans decrease the risks associated with changes in interest rates but involve other risks, primarily because as interest rates rise, the payment by the borrower rises to the extent permitted by the terms of the loan, thereby increasing the potential for default. At the same time, the marketability of the underlying property may be adversely affected by higher interest rates. The Bank believes that these risks, which have not had a material adverse effect on the Bank to date, generally are less than the risks associated with holding fixed-rate loans in an increasing interest rate environment. At March 31, 2006, approximately $529.5 million, or 67.4%, of the Bank’s permanent single-family residential loans held for investment consisted of loans with adjustable interest rates. Also, as interest rates decline, borrowers may refinance their mortgages into fixed-rate loans thereby prepaying the balance of the loan prior to maturity.

      The Bank continues to originate long-term, fixed-rate conventional mortgage loans. The Bank generally sells current production of these loans with terms of 15 years or more to the Federal Home Loan Mortgage Corporation (“FHLMC”), Federal National Mortgage Association (“FNMA”) and other institutional investors, while keeping some of the