When Robert De Niro saw Leonardo DiCaprio's acting in this movie, he called Martin Scorsese to tell him about the kid and he must check him out. Scorsese has since said that this was very unusual as De Niro wouldn't normally have this level of praise for a fellow actor. The three would finally work together in Killers of the Flower Moon (2023).
Leonardo DiCaprio grew a few inches while shooting the film and he had to slouch in several scenes to look smaller next to Robert De Niro.
Tobey Maguire first auditioned for the part of Toby, but director Michael Caton-Jones thought he wasn't right for the role. Leonardo DiCaprio, who is close friends with Maguire, still wanted him to be a part of the film, so he got him the role of Toby's friend Chuck Bolger.
Producer Art Linson knew the film would be a tough sell. When he attended a test screening of the film with the Warner Brothers executives, he asked an old lady what she thought of the film. To his delight, he found out that she loved it. He later found out that the old lady was Robert De Niro's grandmother.
While not Tobey Maguire's movie debut, This Boy's Life (1993) is Maguire's first film in which he has a credited speaking role. Maguire's film debut was actually in The Wizard (1989), but he was uncredited and had no lines.