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): May 6, 2013

WALGREEN CO.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (847) 315-2500

Not Applicable

(Former name or former address, if changed since last report)

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:

Item 7.01. Regulation FD Disclosure.

Walgreen Co. (“Walgreens”) has owned a 45% equity interest in Alliance Boots GmbH (“Alliance Boots”) since August 2, 2012 and has a call option to acquire the remaining 55% equity interest during the six-month period beginning February 2, 2015. Walgreens accounts for its 45% investment in Alliance Boots using the equity method of accounting on a three-month lag basis.

As disclosed in the press release attached as Exhibit 99.1 hereto, Alliance Boots will release its financial results for the year ended March 31, 2013 and publish its annual report on May 15, 2013 at 6:00 a.m. Eastern daylight time. Both documents will be available through www.allianceboots.com. In addition, Alliance Boots will hold a press conference in London on May 15, 2013 at 6:30 a.m. Eastern daylight time to discuss the year’s results. The press conference will be webcast live through www.allianceboots.com.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits. The following exhibit is furnished as part of this Form 8-K:

Cautionary Note Regarding Forward-Looking Statements

Statements in this report that are not historical are forward-looking statements made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Words such as “expect,” “likely,” “outlook,” “forecast,” “would,” “could,” “should,” “can,” “will,” “project,” “intend,” “plan,” “goal,” “continue,” “sustain,” “synergy”, “on track,” “believe,” “seek,” “estimate,” “anticipate,” “may,” “possible,” “assume,” variations of such words and similar expressions are intended to identify such forward-looking statements. These forward-looking statements are not guarantees of future performance and are subject to risks, uncertainties and assumptions that could cause actual results to vary materially from those indicated, including the factors described in Item 1A (Risk Factors) of our most recent Annual Report on Form 10-K and Quarterly Report on Form 10-Q, each of which is incorporated herein by reference, and in other documents that we file or furnish with the Securities and Exchange Commission. Should one or more of these risks or uncertainties materialize, or should underlying assumptions prove incorrect, actual results may vary materially from those indicated or anticipated by such forward-looking statements. Accordingly, you are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date they are made. Except to the extent required by law, Walgreens does not undertake, and expressly disclaims, any duty or obligation to update publicly any forward-looking statement after the date of this report, whether as a result of new information, future events, changes in assumptions or otherwise.

SIGNATURE

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.