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): May 6, 2016

Alder BioPharmaceuticals, Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (425) 205-2900

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 May 6, 2016, Alder BioPharmaceuticals, Inc. (“Alder”) announced that it has licensed the exclusive worldwide rights to clazakizumab to Vitaeris, Inc., a newly formed company that will pursue innovative therapeutic indications in chronic inflammatory diseases (“Vitaeris”). In exchange for the rights to clazakizumab, Alder has received an equity stake in Vancouver, British Columbia, based Vitaeris and is eligible to receive royalties and certain other payments. In addition, Randall C. Schatzman, Ph.D., president and chief executive officer of Alder, has joined Vitaeris’ board of directors.

This Current Report on Form 8-K contains forward-looking statements, including, without limitation, statements relating to: the continued development and clinical, therapeutic and commercial potential of clazakizumab; and Alder’s potential receipt of royalties and other payments under the license agreement with Vitaeris. Words such as “will,” “eligible,” “potential,” or other similar expressions, identify forward-looking statements, but the absence of these words does not necessarily mean that a statement is not forward-looking. In addition, any statements that refer to expectations, projections or other characterizations of future events or circumstances are forward-looking statements. The forward-looking statements in this Current Report on Form 8-K are based upon Alder’s current plans, assumptions, beliefs, expectations, estimates and projections, and involve substantial risks and uncertainties. Actual results and the timing of events could differ materially from those anticipated in the forward-looking statements due to these risks and uncertainties as well as other factors, which include, without limitation: risks related to the potential failure of clazakizumab to demonstrate safety and efficacy in clinical testing; the clinical, therapeutic and commercial value of clazakizumab; risks and uncertainties related to regulatory review and approval processes; and other factors discussed under the caption “Risk Factors” in Alder’s Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2016, which was filed with the Securities and Exchange Commission (SEC) on April 28, 2016, and is available on the SEC’s website at www.sec.gov. Additional information will also be set forth in Alder’s other reports and filings it will make with the SEC from time to time. The forward-looking statements made in this Current Report on Form 8-K speak only as of the date of this Current Report on Form 8-K. Alder expressly disclaims any duty, obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in Alder’s expectations with regard thereto or any change in events, conditions or circumstances on which any such statements are based.

SIGNATURES

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.