Al Pacino's residence in the movie is located at 5-7 Minetta Street in Manhattan's Greenwich Village. The real-life Frank Serpico, however, lived at Perry & Greenwich, a few blocks away.
After spending a lot of time with Pacino as he prepared for the role, the real Serpico wanted to remain on the set during filming. Producer Bregman said he had to hurt Serpico's feelings and ordered him to leave because he believed that his presence would prove a distraction.
John G. Avildsen was originally to direct, but was replaced just before filming due to differences with the producer.
After he decided to make the film, Al Pacino invited Frank Serpico to stay with him at a house that Pacino had rented in Montauk, New York. When Pacino asked Serpico, "Why did you do it?" Serpico replied, "Well, Al, I don't know. I guess I would have to say it would be because... if I didn't, who would I be when I listened to a piece of music?"
Shot on 104 different locations in every borough of New York City except Staten Island.
Woodie King Jr. was originally cast as a hoodlum but broke his leg while filming a chase scene. He was replaced but returned to the set two months later to play Leslie's friend, Larry, in the party scene.
Playwright Sidney Kingsley loaned his apartment to Sidney Lumet for use to film the party scene. In 1935, Kingsley hired an 11-year-old Lumet to appear on Broadway in his play, "Dead End", and they had remained friends since then.
The film was shot in reverse order. Al Pacino began with long hair and a beard, then for each scene, his hair and beard were trimmed bit by bit until he became clean-cut.