James Gandolfini said that he was often contacted by real-life "wise guys," complimenting him on the authenticity of the series, as well as giving him advice.
It is said that during some scenes, James Gandolfini inserted a small stone in his shoe to anger him, making him play the role of Tony Soprano more authentically. He would also stay awake all night for some of the breakfast scenes, to achieve a tired look.
After the pilot aired, a real-life "wise guy" told James Gandolfini never to wear shorts again. The encounter seems to have been incorporated into season four, episode one, "For All Debts Public and Private," when New York City mob boss Carmine tells Tony that he'd heard about his recent backyard party, and that "a don doesn't wear shorts." However real life ex-mob capo and street boss Michael Franzese disputes this claim whereas his father Sonny wore shorts on a regular basis.
Four members of northern New Jersey's only real-life mob family, the DeCavalcantes, were secretly taped in 1999 by federal investigators talking about their similarity to the fictional DiMeo/Soprano crime family. On the tape, one mobster asks another, "Is this supposed to be us?" And his capo buddy replies, "You are in there. They mentioned your name in there."