StanCorp Financial Group (SFG)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D. C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) April 23, 2012

STANCORP FINANCIAL GROUP, INC.

(971) 321-7000

(Registrant’s telephone number, including area code)

No Change

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

On April 23, 2012, StanCorp Financial Group, Inc. issued a press release reporting the Company’s first quarter 2012 financial results. A copy of the press release is attached hereto as exhibit 99.1 and furnished herewith. A copy of the Company’s Statistical Supplement dated March 31, 2012, is attached hereto as exhibit 99.2 and furnished herewith.

Financial measures that exclude after-tax net capital gains and losses and accumulated other comprehensive income (loss) are non-GAAP (Generally Accepted Accounting Principles in the United States) measures. To provide investors with a broader understanding of earnings, the Company provides net income per diluted share excluding after-tax net capital gains and losses, along with the GAAP measure of net income per diluted share, because capital gains and losses are not likely to occur in a stable pattern.

Return on average equity excluding after-tax net capital gains and losses from net income and accumulated other comprehensive income (loss) from equity is furnished along with the GAAP measure of net income return on average equity because management believes providing both measures gives investors a broader understanding of return on equity. Measuring return on average equity without accumulated other comprehensive income (loss) excludes the effect of market value fluctuations of the Company’s fixed maturity securities associated with changes in interest rates and other market data. Management believes that measuring return on average equity without accumulated other comprehensive income (loss) is important to investors because the turnover of the Company’s portfolio of fixed maturity securities may not be such that unrealized gains and losses reflected in accumulated other comprehensive income (loss) are ultimately realized. Furthermore, for the purpose of calculating this ratio, management believes exclusion of accumulated other comprehensive income (loss) provides investors with a better measure of return.

(d) Exhibits

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.