Sylvester Stallone gained 40 pounds to add realism to his portrayal of the police officer. He also was only paid SAG minimum wages. By the time that reshoots were required, he had lost the weight again.
At the end of the film, when Freddy and Gary are bringing in Murray Babitch to the NYC authorities, there is one shot of Moe Tilden coming out of a building. In this one shot, his mustache is noticeably longer. Director James Mangold wanted to get a shot of Robert De Niro's character walking out of the building. De Niro had already completed his scenes and was already working on another film, Jackie Brown. De Niro agreed to return and appear in the shot, but could not trim his longer mustache as it was required for his character, Louis Gara, in Jackie Brown.
William Kalaidjian, who presided at outdoor funeral set, was an N.Y.P.D. chaplain for many years and now ministers to veterans through the Bronx VA hospital.
Deborah Harry acted in the movie but was edited out in the final cut. She explained on a live television special that although she was cut, she still got paid.
Robert Patrick got the part after running into actor Peter Berg and the film's producer and music supervisor, Meryl Poster, who were staying in the same hotel in New York. He got the script and then read for director James Mangold a few days later.
There is a disclaimer at the end of the credits which states "This film is a work of fiction. It is currently illegal for New York City Police officers to live outside the state of New York."
The sandwich scene in Robert De Niro's office was Stallone's first day shooting. The sandwiches, which were an afterthought for the actors' lunch, were improvised into the scene by De Niro.