SECURITIES AND EXCHANGE COMMISSION

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): March 2, 2004

Waste Management, Inc.

Registrant’s Telephone number, including area code: (713) 512-6200

Table of Contents

Item 5. Other Events

     On each of January 21, 2004, February 12, 2004 and March 2, 2004, Waste Management, Inc. (the “Company”) filed prospectus supplements pursuant to Rule 424 of the Securities Act of 1933, as amended, to its registration statement on Form S-3 (No. 333-97697) (the “Registration Statement”), to register the issuance of shares of its common stock, par value $0.01 per share (the “Common Stock”), upon exercise of outstanding warrants of the Company.

     The Company is filing legal opinions issued in connection with these issuances of its shares of Common Stock as exhibits 5.1, 5.2 and 5.3 hereof, to be incorporated by reference into the Registration Statement.

Item 7. Financial Statements, Pro Forma Financial Information and Exhibits

     (c) Exhibits.

SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has caused this report to be signed on its behalf by the undersigned, hereunto duly authorized.

Exhibit Index

EXHIBIT 5.1

[WASTE MANAGEMENT LETTERHEAD]

January 21, 2004

Waste Management, Inc.
1001 Fannin Street, Suite 4000
Houston, Texas 77002

Gentlemen,

     I am Vice President and Assistant General Counsel – Corporate & Securities of Waste Management, Inc., a Delaware corporation (the “Company”), and have acted in such capacity in connection with the sale of 15,295 shares of the Company’s common stock, par value $0.01 per share (the “Common Stock”), pursuant to the exercise of a warrant dated April 26, 1996 (the “Warrant”). The 15,295 shares of Common Stock are being issued under a registration statement on Form S-3 (No. 333-97697) filed under the Securities Act of 1933, as amended.

     I have examined corporate documents of the Company, including its Certificate of Incorporation and Bylaws, and resolutions adopted by its board of directors and committees thereof. I have also examined the Registration Statement, together with the exhibits thereto, and such other documents that I have deemed necessary for the purposes of expressing the opinion contained herein. I have relied on representations made by and certificates of the officers of the Company and public officials with respect to certain facts material to my opinion. I have made no independent investigation regarding such representations and certificates.

     Based upon the foregoing, I am of the opinion that when payment for the shares of Common Stock has been made pursuant to the Warrant, the Common Stock issued thereupon will be validly issued, fully paid and nonassessable.

     I hereby consent to the filing of this opinion as an exhibit to the Registration Statement.

Very truly yours,

/s/ John S. Tsai
John S. Tsai
Vice President & Assistant General
Counsel – Corporate & Securities

EXHIBIT 5.2

[WASTE MANAGEMENT LETTERHEAD]

February 12, 2004

Waste Management, Inc.
1001 Fannin Street, Suite 4000
Houston, Texas 77002

Gentlemen,

     I am Vice President and Assistant General Counsel — Corporate & Securities of Waste Management, Inc., a Delaware corporation (the “Company”), and have acted in such capacity in connection with the sale of 45,590 shares of the Company’s common stock, par value $0.01 per share (the “Common Stock”), pursuant to the exercise of a warrant dated February 18, 1997 (the “Warrant”). The 45,590 shares of Common Stock are being issued under a registration statement on Form S-3 (No. 333-97697) filed under the Securities Act of 1933, as amended.

     I have examined corporate documents of the Company, including its Certificate of Incorporation and Bylaws, and resolutions adopted by its board of directors and committees thereof. I have also examined the Registration Statement, together with the exhibits thereto, and such other documents that I have deemed necessary for the purposes of expressing the opinion contained herein. I have relied on representations made by and certificates of the officers of the Company and public officials with respect to certain facts material to my opinion. I have made no independent investigation regarding such representations and certificates.

     Based upon the foregoing, I am of the opinion that when payment for the shares of Common Stock has been made pursuant to the Warrant, the Common Stock issued thereupon will be validly issued, fully paid and nonassessable.

     I hereby consent to the filing of this opinion as an exhibit to the Registration Statement.

Very truly yours,

/s/ John S. Tsai
John S. Tsai
Vice President & Assistant General
Counsel — Corporate & Securities

EXHIBIT 5.3

[WASTE MANAGEMENT LETTERHEAD]

March 2, 2004

Waste Management, Inc.
1001 Fannin Street, Suite 4000
Houston, Texas 77002

Gentlemen,

     I am Vice President and Assistant General Counsel — Corporate & Securities of Waste Management, Inc., a Delaware corporation (the “Company”), and have acted in such capacity in connection with the sale of 50,000 shares of the Company’s common stock, par value $0.01 per share (the “Common Stock”), pursuant to the exercise of a warrant dated March 17, 1996 (the “Warrant”). The 50,000 shares of Common Stock are being issued under a registration statement on Form S-3 (No. 333-97697) filed under the Securities Act of 1933, as amended.

     I have examined corporate documents of the Company, including its Certificate of Incorporation and Bylaws, and resolutions adopted by its board of directors and committees thereof. I have also examined the Registration Statement, together with the exhibits thereto, and such other documents that I have deemed necessary for the purposes of expressing the opinion contained herein. I have relied on representations made by and certificates of the officers of the Company and public officials with respect to certain facts material to my opinion. I have made no independent investigation regarding such representations and certificates.

     Based upon the foregoing, I am of the opinion that when payment for the shares of Common Stock has been made pursuant to the Warrant, the Common Stock issued thereupon will be validly issued, fully paid and nonassessable.

     I hereby consent to the filing of this opinion as an exhibit to the Registration Statement.

Very truly yours,

/s/ John S. Tsai
John S. Tsai
Vice President & Assistant General
Counsel — Corporate & Securities