Michael Madsen impulsively proposed to, and married, DeAnna Madsen during a two-day break in filming. According to Michael Madsen, Al Pacino was disgusted by his impulsiveness. The Madsens remain happily married.
Donnie bets his kids $20 that they can't get through breakfast without saying three words, and is daughter replies "you lose." The scene is based on a famous incident involving writer Dorothy Parker and President Calvin Coolidge, known as "Silent Cal" for his quiet manner and hatred of small talk. Parker, seated next to Coolidge, turned to him and said "Mr. Coolidge, I've made a bet against a fellow who said it was impossible to get more than two words out of you." Coolidge allegedly replied "You lose."
Joseph D. Pistone said in an interview in the special features on the DVD that he was suppose to be undercover for a few months; it ended up being 6 years. His family was moved across the country after 9 months; he rarely saw them.
During the montage which accompanies the song "Happiness" there is a brief shot of a panel truck exiting a garage bay under the Manhattan Bridge Overpass. The bay is part of Chambers Paper Fibers Corp which was the real-life site of NYPD Det. Rick Cowan's sting operation which took down the Mafia garbage cartels in NYC (Operation Wasteland.) These exploits are detailed in his book "Takedown." The use of the location had to be intentional, the trials of the heads of the garbage cartels occurred in the same year as the film's release, 1997.
The trivia items below may give away important plot points.
The movie ends with the implication that Lefty was killed after being "sent for". In real life, the FBI intercepted Lefty on the way to being killed, and arrested him. Sonny Black was "sent for" and murdered; his body was found on Staten Island a year later. Joe Massino, who orchestrated his murder, was convicted in 2005. Lefty was convicted of conspiracy to commit murder, extortion, distribution of a controlled dangerous substance, and running an illegal gambling operation. He was sentenced to 20 years in prison, but received early parole in 1992 after it he was diagnosed with terminal lung cancer. He died in 1994.
In one of the final scenes, Lefty is seen taking off his jewellery after he has been sent for, knowing he would be killed. In real life, Sonny Black was sent for and killed after he took off his jewellery and gave it to his favorite bartender knowing he would be killed.
Because he was so convincing in his undercover persona, the Bonanno family was seriously considering 'making' Joe Pistone (e.g. fully initiating him into the mob) before they learned he was an FBI agent.