See main article: 2004 NASDAQ-100 Open.
Andy Roddick won the men's singles tennis title at the 2004 Miami Open after Guillermo Coria retired in the final, with the scoreline at 6–7(2–7), 6–3, 6–1.
Andre Agassi was the three-time defending champion, but lost in the fourth round to Agustín Calleri. Agassi's win over Max Mirnyi in the third round was his record 20th consecutive win at the Miami Open.
The third round match between Rafael Nadal and Roger Federer marks the first time they faced each other, eventually meeting on 39 more occasions.
All thirty-two seeds received a bye to the second round.