Originally, in the scene where Cady puts handcuffs on Lori, she was supposed to start freaking out. Illeana Douglas was the one who came up with the idea of having her character laughing and trying to play along instead.
The thick accent Robert De Niro used to play Max Cady reportedly gave Martin Scorsese the creeps. As a joke, De Niro would call Scorsese's house, leaving voicemails as Cady.
The scene in the high school auditorium was shot in one take with two cameras.
Robert De Niro's Cady accent came from an earlier role, where he played a southerner. To prepare for the role, De Niro took excerpts of the script and a tape recorder into southern towns and would ask locals to read the lines into the tape.