When the real Jake LaMotta saw the movie, he said it made him break down in tears and realize for the first time what a terrible person he had been. He asked the real Vicki LaMotta "Was I really like that?". Vicki replied "You were worse."
In 1978, Martin Scorsese was at an all-time low after his last movie New York, New York (1977) had bombed at the box office, followed by a near-overdose resulting from an addiction to cocaine. Robert De Niro visited him at the hospital, and told him that he had to clean himself up and make this movie about a boxer. De Niro had asked Scorsese many times before, but he had always refused (he didn't like sports movies anyway), but due to De Niro's persistence, he eventually gave in. Scorsese believed that his American career was over anyway, so he wanted to do one final film there, and then move to Europe to make smaller movies. Many (including Scorsese) claim that De Niro saved Scorsese's life by getting him back into work, and that this movie cemented Scorsese's reputation as one of the most important American filmmakers of all time.
When Martin Scorsese visited some boxing matches, he was immediately struck by two images: the blood-soaked sponge wiped across the fighter's back, and the pendulous drops of blood hanging off the ropes.
In preparation for his role, Robert De Niro went through extensive physical training, then entered in three genuine Brooklyn boxing matches and won two of them.
Robert De Niro accidentally broke Joe Pesci's rib in a sparring scene. This shot appears in the film: De Niro hits Pesci in the side, Pesci groans, and there is a quick cut to another angle.
Charles Scorsese: Martin Scorsese's father is one of the mob wiseguys crowding the LaMotta brothers at a Copa nightclub table.