Jerry Lewis

Character: Professor Julius F. Kelp / Buddy Love / Baby Kelp

Stella Stevens

Character: Stella Purdy

Del Moore

Character: Dr. Hamius R. Warfield

Henry Gibson

Character: Gibson, College Student

Kathleen Freeman

Character: Millie Lemmon

Richard Kiel

Character: Man in Gym (uncredited)

Norman Alden

Character: Football Player

Howard Morris

Character: Mr. Elmer Kelp

Elvia Allman

Character: Edwina Kelp

Milton Frome

Character: Dr. M. Sheppard Leevee

Doodles Weaver

Character: Rube

Murray Alper

Character: Gym Attendant (uncredited)

Buddy Lester

Character: Bartender

Med Flory

Character: Football Player

Seymour Cassel

Character: Bored Man

Stephanie Hill

Character: Waitress (uncredited)

Marvin Kaplan

Character: English Student

Skip Ward

Character: Football Player

Billy Bletcher

Character: Plumber (uncredited)

Robert Donner

Character: College Student (uncredited)

Art Gilmore

Character: Narrator (voice) (uncredited)