According to Christopher Lloyd, after filming the scene where his character spears Gunther's apple with a knife and eats it, Hank Johnston, the young actor playing the role, was so frightened of Lloyd that he wouldn't approach him afterwards on the set.
During his first audition, Mason Gamble pulled a live worm out of his pocket. This spontaneous move inspired the casting directors to cast him.
Over 20,000 little boys auditioned for the titular role of Dennis Mitchell. Ten were selected to test the role with Walter Matthau.
Leslie Nielsen was offered the role of Mr. Wilson. He had to turn it down because he was committed to Surf Ninjas (1993).
Jeannie Russell: One of the Mitchells' neighbors. Russell had originally played the role of Dennis Mitchell's nemesis Margaret Wade on the classic TV series Dennis, Geschichten eines Lausbuben (1959).