Gene Hackman almost passed on this film. He felt that the length of time between the original and the sequel would hurt the film's chances for success. In the DVD commentary Hackman suggested this was the reason for the film's disappointing box office performance.
Doyle's memorable cry of "Mickey Mantle sucks!" during the cold turkey sequence was the source of much trouble for the film makers and their legal department. Producer Robert L. Rosen had to track down Mickey Mantle to obtain his permission for the reference. After a long phone call, Rosen flew out to Mantle's home in Dallas with a print of the film, which was screened for him and his lawyer. When Gene Hackman uttered the line, Mantle surprised Rosen not only by roaring with laughter but also insisting that they watch the rest of the film because both he and his lawyer were enjoying it so much. Mantle later happily signed a release waiver and the line stayed in the film.
Alain Charnier's villa is the same building used in the original film, The French Connection (1971).
For the French version of the film the character of Popeye was given a thick American accent in order to allow sequences where he encounters linguistic problems to make sense, but not without occasional absurdities. For example, he has no trouble arguing extensively and in an articulate way in French with local policemen, but can't find a decent way to order a simple glass of whiskey.
This is the first movie in Hollywood history to have a title and just a number after it (i.e., 2). The Godfather Part II was the first sequel to have a number in it, but that was proceeded by "Part."