Jodie Foster was originally signed to play Michael Douglas's sibling in the film. However, Foster changed her mind and wanted to appear as Douglas's daughter instead. Douglas and director David Fincher were very opposed to this change so the part went to Sean Penn instead. Foster promptly sued PolyGram to the tune of $54.5 million - even though her Egg Pictures was one of the film's production companies. The matter was fortunately settled out of court. Douglas - who is a personal friend of Foster - said that it didn't seem right for him to play Foster's father, given that there is only 17 years age difference between the two. Ironically, Douglas HAS already played Foster's father - he did so in the Disney film Napoleon and Samantha (1972) at the start of both of their careers.
Nicholas's "San Francisco" home was actually the historic Filoli Mansion, 25 miles south of San Francisco in Woodside, California. The plain gravel forecourt of the mansion was made to look more like a wrap-around driveway by the addition of the fountain, which was constructed of lightweight foam. The interior shots of the kitchen were made in the original time-worn kitchen, which is displayed on tours but no longer used. The kitchen's state of repair is not good, which partially accounts for the very dim lighting used in the kitchen scenes. The scenes in which the walls were defaced with graffiti was done by tacking up lightweight graffiti-painted foamcore boards over the wood paneling. All of the scenes at the mansion were completed in one day.
David Fincher claimed in an interview, in UK film magazine Empire, that there is a can of haggis in every scene of the movie. This was done as a joke, because "Haggis" is the nickname of cinematographer Harris Savides.
In searching for a perfect engine sound for Nicholas' 7 series BMW, one member of the sound editing team located in Sausalito, CA actually borrowed his high school friend's Dinan modified BMW 540 for half day.
Among the tests that Nicholas is asked to take when he interviews at CRS is the MMPI. This is the Minnesota Multiphasic Personality Inventory which is one of the most commonly used personality tests in mental health. The test is used by trained professionals to assist in identifying personality structure and psychopathology.
Conrad's use of the pseudonym Seymour Butts and Nicholas' response of, "'Under the Bleachers' by Seymour Butts", is a reference to the joke series "A Book Never Written" featured in Boys' Life (the official magazine of the Boy Scouts of America).
The trivia items below may give away important plot points.
The scene in which Nicholas wakes up in a crypt in Mexico is an homage to the film Bring Me the Head of Alfredo Garcia (1974), in which protagonist Bennie is buried alive in a Mexican cemetery and must claw his way out of a shallow grave. Nicholas' kidnappers even re-dress him in the same suit that Bennie wears through the duration of that film.