Both Liza Minnelli and Martin Scorsese have said that virtually all of the dialogue in the film was improvised. This created later difficulty during the editing phase, as the director and editors struggled to create a streamlined narrative.
The original song titled "Theme from New York, New York" was scrapped at the insistence of Robert De Niro. Grudgingly, John Kander and Fred Ebb wrote a new version, which has since become one of the most famous and often recorded songs in history. Kander and Ebb have often expressed extreme gratitude to De Niro for his influence.
Originally four and a half hours long. Director Martin Scorsese cut it to 153 minutes, then to 136 minutes. In 1981 some material (mainly the 'Happy Endings' sequence) was restored and the film became 163 minutes long.
Liza Minnelli used her mother's (Judy Garland's) old dressing room, her mother's old hairdresser (Sydney Guilaroff) and worked on mother's old MGM sound stages during the filming of this. Additionally, during interviews she did her mother's famous "oh-uh, ah, ohs" with hand gestures.
Although Robert De Niro did learn the basic technique of how to play the saxophone, the sax music on the soundtrack was dubbed in by cast member Georgie Auld. This movie introduces the song "New York, New York" that later became a pop music standard.
Hollywood producer Julia Phillips has a silent bit part in the opening sequence, flirting with Robert De Niro in a nightclub. When the scene was finished she asked to keep her costume, (a black evening gown), and was put out when Scorsese made her write a check for it.