The film is an Italian–American[4] venture produced by The Ladd Company, Embassy International Pictures, PSO Enterprises and Rafran Cinematografica, and distributed by Warner Bros. Based on Harry Grey's novel The Hoods, it chronicles the lives of best friends David "Noodles" Aaronson and Maximilian "Max" Bercovicz as they lead a group of Jewish ghetto youths who rise to prominence as Jewish gangsters in New York City's world of organized crime.

The film explores themes of childhood friendships, love, lust, greed, betrayal, loss, and broken relationships, together with the rise of mobsters in American society.

The original "European cut" has remained a critical favourite and frequently appears in lists of the greatest films of all time, especially in the gangster genre.

Noodles is drugging himself in an opium den with a newspaper next to him featuring the death of bootleggers Patrick Goldberg, Philip Stein and Maximilian Bercovicz.

In the 1920s, David "Noodles" Aaronson leads a gang of him and his three friends "Patsy" Goldberg, "Cockeye" Stein and Dominic, performing jobs for local gangster Bugsy.

Upon regaining consciousness, Noodles learns that Max, Patsy, and Cockeye have been killed by the police during the heist, as established at the beginning of the film.

In an interview by Noël Simsolo published in 1987, Leone lent support to this interpretation, saying that the scenes set in the 1960s could be seen as an opium dream of Noodles'.

[12] The cast also includes Noah Moazezi as Dominic, James Russo as Bugsy, producer Arnon Milchan as Noodles' chauffeur, Marcia Jean Kurtz as Max's mother, Joey Faye as an "adorable old man", and Olga Karlatos as a wayang patron.

Frequent De Niro collaborator Chuck Low and Leone's daughter Francesca respectively make uncredited appearances as Fat Moe (and Deborah's father), and as David Bailey's girlfriend.

and Once Upon a Time in America, Leone turned down an offer from Paramount Pictures to direct The Godfather in order to pursue his pet project.

[15][16] At some point Leone considered other colleagues including Miloš Forman and John Milius for the role of director, with him just serving as producer.

[21] After Grimaldi bought the rights, he felt that he needed an American scriptwriter to faithfully capture the spirit of the novel; he eventually made a deal with Norman Mailer, whose draft greatly disappointed both Grimaldi and Leone, who later described Mailer's draft as 'a Mickey Mouse version [of the novel]' that lacked in structure and 'made no sense at all'.

[26] At this stage, Leone's casting ideas included Tom Berenger, Dustin Hoffman, Paul Newman and Liza Minnelli.

[29] In 1981, at Milchan's suggestion, Leone met Robert De Niro and eventually offered him a role of his choice between Noodles and Max.

[32] Elizabeth McGovern was chosen for the role of Deborah against De Niro's request for having a New York native with a Brooklyn accent, due to Leone's appreciation of her performance in Ragtime.

[32] Tuesday Weld was cast as Carol, a role that Leone had previously envisioned for Claudia Cardinale, at De Niro's recommendation.

[37] The New York's railway "Grand Central Station" scene in the thirties flashbacks was filmed in the Gare du Nord in Paris.

[38] Shooting in New York proved to be difficult, as the IATSE labor union raised a strong controversy over Leone's use of a foreign crew, and launched such a massive public protest campaign that President Ronald Reagan called for a Department of Labour investigation into the matter.

[40] After a few weeks Nilo Jacoponi, Manlio Rocchetti and Gino Zamprioli replaced Christopher Tucker, whose make-up was considered excessive and unrealistic by Leone.

[50] In the United States, a heavily edited version of the film received a wide release in 894 theaters on June 1, 1984, and grossed $2.4 million during its opening weekend.

One among them later confronted Robert De Niro in a press conference and made harsh comments to the film's depiction, describing it as "blatant, gratuitous violence".

Because of this early audience reaction, the fear of its length, its graphic violence, and the inability of theaters to have multiple showings in one day, The Ladd Company cut entire scenes and removed approximately 90 minutes of the film,[23] without the supervision of Sergio Leone.

Noodles' 1968 meeting with Deborah was excised, and the scene with Bailey ends with him shooting himself (with the sound of a gunshot off screen) rather than the garbage truck conclusion of the 229-minute version.

[69] On September 30, 2014, Warner Bros. released a two-disc Blu-ray and DVD set of the 251-minute restoration shown at the 2012 Cannes Film Festival, dubbed the Extended Director's Cut.

[12] Furthermore, he gave the American theatrical version one star out of four, calling it "an incomprehensible mess without texture, timing, mood, or sense".

[76] Ebert, in his review of Brian De Palma's The Untouchables, called the original uncut version of Once Upon a Time in America the best film depicting the Prohibition era.

[60] Some were critical towards the movie's graphic violence and cruelty, with Donald Clarke of The Irish Times condemning it as a "fistful of misogyny" and "offensively sexist".

The website's critic consensus reads: "Sergio Leone's epic crime drama is visually stunning, stylistically bold, and emotionally haunting, and filled with great performances from the likes of Robert De Niro and James Woods.

"[81] When Sight & Sound asked several UK critics in 2002 what their favorite films of the last 25 years were, Once Upon a Time in America placed at number 10.

[86] The film's music was disqualified from Oscar consideration for a technicality,[87] as the studio accidentally omitted the composer's name from the opening credits when trimming its running time for the American release.