2004 Gerry Weber Open – Singles

Roger Federer was the defending champion, and won in the final 6–0, 6–3 against Mardy Fish. It was his second singles title in Halle. He did not lose a single set in the entire tournament.

Seeds
A champion seed is indicated in bold text while text in italics indicates the round in which that seed was eliminated.

• # Roger Federer (champion)

• # 🇩🇪 Rainer Schüttler (semifinals)

• # 🇨🇿 Jiří Novák (semifinals)

• # Martin Verkerk (first round)

• # 🇷🇺 Marat Safin (first round)

• # 🇺🇸 Mardy Fish (final)

• # 🇷🇴 Andrei Pavel (first round)

• # 🇪🇸 Feliciano López (first round)