Leonardo DiCaprio called his one-on-one scene with Jack Nicholson "one of the most memorable moments of my life."
Vera Farmiga met with a real LAPD psychiatrist to prepare for her role. The psychiatrist read the script, and told Farmiga that Madolyn did pretty much everything wrong.
Mark Wahlberg easily fell back on his native accent. Martin Scorsese joked it was so thick, they'd need subtitles.
Roughly half of the $90 million budget went to the actors' salaries.