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