The 2004 Tennis Masters Cup was a men's tennis tournament played on outdoor hard courts.

It was the 35th edition of the year-end singles championships, the 30th edition of the year-end doubles championships, and was part of the 2004 ATP Tour.

It took place at the Westside Tennis Club in Houston, Texas, United States, from November 13 through November 21, 2004.

Roger Federer won the singles title.

Roger Federer defeated Lleyton Hewitt, 6–3, 6–2 Bob Bryan / Mike Bryan defeated Wayne Black / Kevin Ullyett, 4–6, 7–5, 6–4, 6–2 1 Malisse and Rochus qualified due to winning French Open and a top 20 finish according to the rules