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): July 24, 2020

Registrant’s telephone number, including area code: (732) 329-8885

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 (see General Instruction A.2. below):

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

Indicate by check mark whether the registrant is an emerging growth company as defined in as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ¨

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 13(a) of the Exchange Act. ¨

On July 24, 2020, CytoSorbents Corporation, a Delaware corporation (the “Company”), completed its previously announced underwritten public offering (the “Offering”) made pursuant to the Underwriting Agreement, dated as of July 21, 2020, by and among Cowen and Company, LLC and SVB Leerink LLC, as representatives of the several underwriters named therein (the “Underwriters”). On July 22, 2020, the Underwriters notified the Company that they had exercised their option to purchase an additional 789,473 shares of common stock, $0.001 par value per share (the “Common Stock”) in full. After giving effect to the full exercise of the Underwriters’ option, the Company issued and sold an aggregate 6,052,631 shares of Common Stock in the Offering, pursuant to the Company’s existing shelf registration statement on Form S-3 (File No. 333-226372). The Company received gross proceeds of approximately $57.5 million, before deducting the underwriting discounts and commissions and fees and expenses payable by the Company in connection with the Offering. Cowen and SVB Leerink acted as joint book-running managers for the Offering. B. Riley FBR acted as co-manager for the Offering.

(d) Exhibits

SIGNATURE

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.

Exhibit 5.1

July 24, 2020

CytoSorbents Corporation

7 Deer Park Drive, Suite K

Monmouth Junction, NJ 08852

Ladies and Gentlemen:

We have acted as counsel for CytoSorbents Corporation, a Delaware corporation (the “Company”), in connection with the offering and sale by the Company of 6,052,631 shares (the “Shares”) of common stock, $0.001 par value per share, of the Company pursuant to that certain Underwriting Agreement, dated July 21, 2020, by and among the Company and Cowen and Company, LLC and SVB Leerink LLC, as representatives of the several underwriters named therein (the “Underwriting Agreement”).

In connection with this opinion letter, we have examined the Company’s registration statement on Form S-3 (Registration No. 333-226372) (the “Registration Statement”) which was previously filed with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”) on July 16, 2018, amended by a pre-effective amendment filed by the Company on August 3, 2018 and declared effective by the Commission on August 7, 2018, the Prospectus Supplement, dated July 21, 2020 (the “Prospectus Supplement”) and the accompanying base prospectus dated August 7, 2018 (the “Base Prospectus”) and originals, or copies certified or otherwise identified to our satisfaction, of the Second Amended and Restated Certificate of Incorporation, as amended, the Amended and Restated Bylaws of the Company, the Underwriting Agreement, and such other documents, records and other instruments as we have deemed appropriate for purposes of the opinion set forth herein.

We have assumed the genuineness of all signatures, the legal capacity of all natural persons, the authenticity of the documents submitted to us as originals, the conformity with the originals of all documents submitted to us as certified, facsimile or photostatic copies and the authenticity of the originals of all documents submitted to us as copies.

Based upon the foregoing, we are of the opinion that the Shares, when issued and sold by the Company and delivered by the Company against receipt of the purchase price therefor, in the manner contemplated by the Prospectus Supplement and the Underwriting Agreement will be validly issued, fully paid and non-assessable.

Our opinion is limited solely to the Delaware General Corporation Law without regard to choice of law, to the extent that the same may apply to or govern the transactions contemplated by the Registration Statement. We express no opinion as to the effect of events occurring, circumstances arising, or changes of law becoming effective or occurring, after the date hereof on the matters addressed in this opinion.

We hereby consent to the use of this opinion as Exhibit 5.1 to the Registration Statement and to the reference to us under the caption “Legal Matters” in the Prospectus Supplement. In giving such consent, we do not hereby admit that we are acting within the category of persons whose consent is required under Section 7 of the Securities Act or the rules or regulations of the Commission thereunder.

Very truly yours,