As filed with the United States Securities and Exchange Commission on April 2, 2026

Registration No. 333-284266

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION 

Washington, D.C. 20549

POST-EFFECTIVE AMENDMENT NO. 2
TO 

FORM S-1

ON FORM S-3

REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

Adagio Medical Holdings, Inc.

(Exact name of registrant as specified in its charter)

26051 Merit Circle, Suite 102
Laguna Hills, California 92653
(949) 348-1188

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

Todd Usen
Chief Executive Officer
26051 Merit Circle, Suite 102
Laguna Hills, California 92653
(949) 348-1188

(Name, Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent for Service)

Copies to:
Eric Blanchard
Paul Alexander
Cooley LLP
500 Boylston Street
14th Floor
Boston, MA 02116
(617) 937-2300

Approximate date of commencement of proposed sale to the public:

From time to time after the effective date of this registration statement.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box: ¨

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box: x

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(c) under the Securities Act, check the following box. ¨

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. ¨

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

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until this registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

EXPLANATORY NOTE

This Post-Effective Amendment No. 2 to the Registration Statement on Form S-1 on Form S-3 (File No. 333-284266) (“Post-Effective Amendment No. 2”) of Adagio Medical Holdings, Inc. is being filed solely to amend the Post-Effective Amendment No. 1 to the Registration Statement filed with the U.S. Securities and Exchange Commission on April 1, 2026, to correct Exhibit 23.4, the Consent of Independent Registered Public Accounting Firm. The original filing mistakenly included an unsigned version of the consent of WithumSmith+Brown, PC. No other changes have been made to the Registration Statement. This Post-Effective Amendment No. 2 does not modify any provision of the prospectus that forms part of the Registration Statement and, accordingly, the prospectus has not been included herein. This Post-Effective Amendment No. 2 is not intended to amend or delete any part of the Registration Statement except as specifically noted herein.

PART II
INFORMATION NOT REQUIRED IN PROSPECTUS

Item 16. Exhibits

* Filed herewith. 

† Certain of the exhibits and schedules to this Exhibit have been omitted in accordance with Regulation S-K Item 601. The Company agrees to furnish a copy of all omitted exhibits and schedules to the SEC upon its request. 

# Indicates a management contract or compensatory plan, contract or arrangement.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this Post-Effective Amendment No. 2 to Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized in Laguna Hills, California, on this 2nd day of April, 2026.

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed by the following persons in the capacities and on the dates indicated.