What Hollywood production of the Mafia tells the truth?

 What Hollywood production of the Mafia tells the truth?

As I type this, the answers mention the excellent gangster films A Bronx Tale, Goodfellas, and Casino. However, we also need to keep in mind Donnie Brasco if we're seeking for one that accurately tells the tale.

Donnie Brasco is a very accurate portrayal of life within the American LCN Mafia in addition to being based on the true account of FBI agent Joe Pistone's time spending a significant amount of time deep undercover in the Bonanno Crime Family.There are no opulent homes and tuxedo-clad criminal masterminds or endearing professional assassins living in this realm. No, it's a nasty, lowbrow, clever, but not particularly intelligent society where thugs are always hustling and racing to progress within their own lethal version of a corporate bureaucracy.

Donnie Brasco and "Lefty" Ruggiero in real life