Robert Downey Jr. publicly admitted to using heroin during the making of this film. Jodie Foster wrote him a letter praising his work but warning him that he could not keep doing this on other films.
When Claudia is in the basement in her sister's house, the Step (piece of exercise equipment next to the Stair Climber) has carpet taped to the top. Later, as she leaves, the carpet has vanished.
Russell 'Sad Sack' Terziak: Well, duty calls. Merry Christmas, if I don't ever see you again. You have a nice life, Claudia. (leaves. Claudia walks past Tommy and Leo, nearly in tears)