UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K/A

(Amendment No. 1)

(Mark One)

For the fiscal year ended June 30, 2015

For the transition period from                      to                     

Commission file number: 0-26642

MYRIAD GENETICS, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (801) 584-3600

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

Securities registered pursuant to Section 12(g) of the Exchange Act: None

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

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

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  x    No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  x    No  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of 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 this Form 10-K or any amendment to this Form 10-K.  x

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

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

The aggregate market value of the registrant’s common stock held by non-affiliates of the registrant (without admitting that any person whose shares are not included in such calculation is an affiliate), computed by reference to the price at which the common stock was last sold on December 31, 2014, the last business day of the registrant’s most recently completed second fiscal quarter, was $2,424,609,397.

As of July 31, 2015 the registrant had 68,604,579 shares of common stock outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

The following documents (or parts thereof) are incorporated by reference into the following parts of this Amendment No. 1 to the Annual Report on Form 10-K/A: Certain information required in Part III of this Amendment No. 1 to the Annual Report on Form 10-K/A is incorporated from the Registrant’s Proxy Statement, to be filed no later than 120 days following June 30, 2015, for the Annual Meeting of Stockholders to be held on December 3, 2015.

EXPLANATORY NOTE

We are filing this Amendment No. 1 on Form 10-K/A (this “Amendment”) to amend our Annual Report on Form 10-K for the year ended June 30, 2015 (the “Original Filing”), originally filed with the Securities and Exchange Commission (the “SEC”) on August 12, 2015 (the “Original Filing Date”), solely to re-file the Exhibit List included therein to correct various typographical errors, including the date of the filing from which our current Restated By-Laws is incorporated by reference.

Although the Exhibit List and the corresponding Item 15 from the Original Filing are restated in their entirety, no other changes have been made to the Original Filing except as described above, and this Amendment does not modify, amend, or update in any way any of the financial or other information contained in the Original Filing. This Amendment does not reflect events that may have occurred subsequent to the Original Filing Date. Accordingly, this Amendment should be read in conjunction with the Original Filing and with our filings with the SEC subsequent to the Original Filing Date.

Pursuant to Rule 12b-15 under the Securities Exchange Act of 1934, as amended, this Amendment also contains new certifications pursuant to Section 302 of the Sarbanes-Oxley Act of 2002, which are attached hereto. Because no financial statements have been included in this Amendment and this Amendment does not contain or amend any disclosure with respect to Items 307 and 308 of Regulation S-K, paragraphs 3, 4, and 5 of the certifications have been omitted.

PART IV

See “Index to Consolidated Financial Statements” at Item 8 of the Original Filing.

The following schedule was filed as part of the Original Filing:

Schedule II - Schedule of Valuation and Qualifying Accounts for the Years Ended June 30, 2015, 2014 and 2013.

Other financial statement schedules have not been included because they are not applicable or the information is included in the financial statements or notes thereto.

The exhibits which are filed with or incorporated by reference into this Amendment No. 1 to the Annual Report on Form 10-K/A are set forth in the Exhibit Index beginning on page A-1, which is incorporated herein by reference.

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the Registrant has duly caused this Amendment No. 1 to Annual Report on Form 10-K/A to be signed on its behalf by the undersigned, thereunto duly authorized.

Date: October 2, 2015

EXHIBIT INDEX