Other mistake: Several close-ups of the business cards of Patrick Bateman and his associates reveal a misspelling of the word "Acquisitions" (the "c" is missing - not a small error, given that this is the name of their department).
Visible crew/equipment: In the scene after Patrick Bateman's second encounter with the detective in his office, we see Bateman having sex at Courtney's apartment. After he rolls off her, Bateman approaches the large, stand-up mirror in the bedroom. In the upper right hand corner of the mirror, a boom microphone can clearly be seen moving around to pick up Christian Bale's lines. The next time we get the same long shot, the microphone is gone.
Continuity mistake: In the scene where Patrick is in his office working on a crossword puzzle before talking to Jean, he is writing with his right hand. When the shot changes to the reflection of Patrick's glasses, the reflection shown is as if he is using his left hand. The reflection isn't a mirror image as it should be.
When Bateman in the end of the movie confesses his murders to the answering machine, he mentions murders like a man with a dog and a girl with a nail gun. Those are all murders described very graphically in the book.
Leonardo DiCaprio was originally tapped to play the role of Patrick Bateman, however his agents felt that the role was to twisted and may hurt his image with his younger fans. He ended up passing on the role.
Patrick Bateman: I don't want to get you drunk, but, ah, that's a very fine Chardonnay you're not drinking.
Patrick Bateman: Harold, it's Bateman, Patrick Bateman. You're my lawyer so I think you should know: I've killed a lot of people. Some girls in the apartment uptown, uh, some homeless people maybe 5 or 10, um, an NYU girl I met in Central Park. I left her in a parking lot behind some donut shop. I killed Bethany, my old girlfriend, with a nail gun, and some man, uh, some old faggot with a dog last week. I killed another girl with a chainsaw, I had to, she almost got away, and, uh, someone else there I can't remember, maybe a model, but she's dead too. And Paul Allen. I killed Paul Allen with an axe in the face, his body is dissolving in a bathtub in Hell's Kitchen. I don't want to leave anything out here. I guess I've killed maybe 20 people, maybe 40. I have tapes of a lot of it, uh, some of the girls have seen the tapes. I even, um... I ate some of their brains, and I tried to cook a little. Tonight I, uh, I just had to kill a LOT of people. And I'm not sure I'm gonna get away with it this time. I guess I'll uh, I mean, ah, I guess I'm a pretty uh, I mean I guess I'm a pretty sick guy. So, if you get back tomorrow, I may show up at Harry's Bar, so you know, keep your eyes open.