UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 10-Q/A

(Amendment No. 1)

(Mark One)

For the quarterly period ended September 30, 2011

For the transition period from              to             

Commission File Number: 001-15317

ResMed Inc.

(Exact name of registrant as specified in its charter)

Delaware

(State or other jurisdiction of incorporation or organization)

98-0152841

(I.R.S. Employer Identification No.)

9001 Spectrum Center Blvd.

San Diego, CA 92123

United States of America

(Address of principal executive offices)

(858) 836-5000

(Registrant’s telephone number, including area code)

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

At October 25, 2011, there were 147,092,208 shares of Common Stock ($0.004 par value) outstanding. This number excludes 19,206,473 shares held by the registrant as treasury shares.

RESMED INC. AND SUBSIDIARIES

Explanatory Note

This Amendment No. 1 on Form 10-Q/A is an amendment to the Registrant’s Quarterly Report on Form 10-Q for the period ended September 30, 2011 (the “Report”) filed with the Securities and Exchange Commission on November 3, 2011. This Form 10-Q/A is being filed for the sole purpose of correcting an error on the cover page in the number of shares outstanding of the Registrant’s common stock as of October 25, 2011 which should be 147,092,208 instead of 166,298,681 as the reported number incorrectly included the 19,206,473 shares held as treasury shares. In addition, the Registrant is also including Exhibits 31.1 and 31.2, as required by the filing of this Form 10-Q/A. This Form 10-Q/A does not alter any other part of the content of the Report and does not affect the information originally set forth in the Report, the remaining portions of which have not been amended.

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RESMED INC. AND SUBSIDIARIES

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.

November 21, 2011

ResMed Inc.

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RESMED INC. AND SUBSIDIARIES

Exhibits

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