Jerry Lewis as Professor Julius F. Kelp / Buddy Love / Baby Kelp

Stella Stevens as Stella Purdy

Del Moore as Dr. Hamius R. Warfield

Henry Gibson as Gibson, College Student

Kathleen Freeman as Millie Lemmon

Richard Kiel as Man in Gym (uncredited)

Norman Alden as Football Player

Howard Morris as Mr. Elmer Kelp

Elvia Allman as Edwina Kelp

Milton Frome as Dr. M. Sheppard Leevee

Doodles Weaver as Rube

Murray Alper as Gym Attendant (uncredited)

Buddy Lester as Bartender

Med Flory as Football Player

Seymour Cassel as Bored Man

Stephanie Hill as Waitress (uncredited)

Marvin Kaplan as English Student

Skip Ward as Football Player

Billy Bletcher as Plumber (uncredited)

Robert Donner as College Student (uncredited)

Art Gilmore as Narrator (voice) (uncredited)