According to one of the featurettes on the DVD, Stephen King called this film the single most faithful adaptation of his work.
Fifteen mice were used in the movie. Each spent months being trained to do different tricks.
Many times the actors are looking at a laser pointing at the floor and not a mouse.
At around 1h 35 mins, Tom Hanks wasn't pretending to wipe his jacket. The mouse really defecated on him in the scene.
Tom Hanks accepted the role of Paul Edgecomb as a favor to Frank Darabont, after he was forced to turn down the role of Andy Dufresne in Sueño de fuga (1994), in order to play the title role in Forrest Gump (1994).