UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 10-Q/A

(Mark One)

For the quarterly period ended: June 30, 2012

For the transition period from              to             

Commission file number: 001-31533

DUSA PHARMACEUTICALS, INC.

(Exact Name of Registrant as Specified in Its Charter)

(978) 657-7500

(Registrant’s Telephone Number, Including Area Code)

(Former Name, Former Address and Former Fiscal Year, if Changed Since Last Report)

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 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

As of August 1, 2012, the registrant had 25,001,008 shares of Common Stock, no par value per share, outstanding.

EXPLANATORY NOTE

The sole purpose of this Amendment No. 1 to the Quarterly Report on Form 10-Q of DUSA Pharmaceuticals, Inc. for the quarterly period ended June 30, 2012, filed with the Securities and Exchange Commission on August 2, 2012 (the “Form 10-Q”), is to furnish Exhibit 101 in accordance with Rule 405 of Regulation S-T. Exhibit 101 to this report provides the consolidated financial statements and related notes from the Form 10-Q formatted in XBRL (eXtensible Business Reporting Language), which did not properly merge in the original XBRL transmission.

No other changes have been made to the Form 10-Q. This Amendment No. 1 to the Form 10-Q speaks as of the original filing date of the Form 10-Q, does not reflect events that may have occurred after the original filing date and does not modify or update in any way disclosures made in the original Form 10-Q.

Pursuant to Rule 406T of Regulation S-T, the interactive data files on Exhibit 101 hereto are deemed not filed for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, and otherwise are not subject to liability under those sections.

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 thereunto duly authorized.

Dated: August 2, 2012

Dated: August 2, 2012

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