In 1979, Stern made his film debut as Cyril in "Breaking Away". The following year he played a student who raised objections during Jill Clayburgh's proof of the snake lemma in the film "It's My Turn". He was the novice observer Richard Lymangood in the 1983 action thriller film "Blue Thunder". He had another early film role in the 1984 horror film "C.H.U.D.", as the soup kitchen C.H.U.D. hunter. His breakthrough role as Laurence "Shrevie" Schreiber came in Barry Levinson's "Diner". He appeared in two films with Woody Allen, "Stardust Memories" and "Hannah and Her Sisters".