Ross Bagdasarian Jr.

as Alvin / Simon / David Seville (voice)

Janice Karman

as Theodore / Tommy's Sister (voice)

Frank Welker

as Santa Claus / Doctor (voice)

Charles Berendt

as Clyde Crashcup (voice)

R.J. Williams

as Tommy Waterford (voice)

June Foray

as Mrs. Waterford / Mrs. Claus