Along with top-billed Gleason and Channing, "Skidoo" stars Frankie Avalon, Fred Clark (who died on December 5, two weeks before the film's release), Michael Constantine, Frank Gorshin, John Phillip Law, Peter Lawford, Burgess Meredith, George Raft, Cesar Romero, Mickey Rooney and Groucho Marx playing "God" (making, at age 77, his final appearance in a feature film). Singer-songwriter Nilsson, who wrote the score and receives credit as a member of the cast, appears in a few brief scenes with Fred Clark, as both portray prison tower guards swaying to Nilsson's music while under the influence of LSD.