Boxer Paolo Roberto is featured as a character in the original novel and plays himself in the movie. This is quite possibly only the fourth time in film and literature that this has happened. Previously, Richard Kiley was the tour guide voice in the movie Jurassic Park (1993), having been identified as such in Michael Crichton's novel. Lady Chablis played herself in Mezzanotte nel giardino del bene e del male (1997) after being a character in the original non-fiction book by John Berendt. Finnish painter Kimmo Kaivanto played himself in Jäähyväiset presidentille (1987) after being a character in the original novel by Pentti Kirstilä.
At the time he was approached to play himself in the movie, Paolo Roberto hadn't known the novel featured him as a character.
The role of Ronald Niederman is played by Micke Spreitz. Spreitz got the part after the filmmakers' original choice Dolph Lundgren turned the role down. If Lundgren had taken the part, it would have been his first role in a film from his native country, Sweden.
The name on Salander's apartment door, V. Kulla, is a reference to writer Astrid Lindgren's fictional character Pippi Longstocking and her house Villa Villekulla.
In the early scene where the editors are meeting in the Millennium office, there's a pile of magazines. Prominently displayed is a copy of EXPO, the anti-fascist magazine Stieg Larsson helped found in 1995.