When filming was completed, the footage ran to a total of eight to ten hours. Director Sergio Leone and editor Nino Baragli trimmed the footage to around six hours, with the plan of releasing the film as two three-hour movies. The producers refused this idea, and Leone had to further cut the film down to three hours and forty-nine minutes.
A few days before the film's premiere in 1984, Treat Williams found out the two-hour version, not the three hour and forty-nine minute version, would be shown in theaters. He was heard to have said that no one would understand the movie in the shortened version. Indeed, the film did not do well at theaters, and was shut out of the Oscars, and received no nominations. When the video cassette and DVD versions were released in the original three hour and forty-nine minute version, the film ultimately found commercial and critical success.
Robert De Niro requested a private meeting with renowned crime boss Meyer Lansky to prepare for his role as David "Noodles" Aaronson. The request was denied.
Robert De Niro was the first person cast, having been approached for a role as David "Noodles" Aaronson during filming The Godfather Part II (1974), and was later actively involved with choosing the remaining cast members.