After several takes that never looked quite right, Faye Dunaway got annoyed and told Jack Nicholson to actually slap her. He did and felt very guilty for it, despite it being Dunaway's decision. The shot made it into the movie.
Roman Polanski said that in staying true to the tradition of Raymond Chandler's detective stories, he shot the whole movie from the perspective of the main character.
At the time of filming, Jack Nicholson had just embarked on his longstanding relationship with Anjelica Huston. This made his scenes with her father, John Huston, rather uncomfortable, especially as the only time Anjelica was on set was the day they were filming the scene where Noah Cross interrogates Nicholson's character with "Mr. Gittes...do you sleep with my daughter?"
At one point, Roman Polanski and Jack Nicholson got into such a heated argument that Polanski smashed Nicholson's portable television with a mop. Nicholson used the television to watch Los Angeles Lakers' basketball games and kept stalling shooting.
Screenwriter Robert Towne was originally offered $125,000 to write a screenplay for El gran Gatsby (1974), but Towne felt he couldn't do better than the F. Scott Fitzgerald novel and accepted $25,000 to write his own story, "Chinatown," instead.
C.O. Erickson: The film's executive producer plays the banker in the barbershop who starts an argument with Jake.
Roman Polanski: Although he liked the idea of doing a cameo in the film as the hood who slits Jack Nicholson's nose, he was less thrilled about having to have his long hair cut off for his brief appearance in the film.