Victor Buono as Leo Kroll

David McLean as Lt. Frank Benson

Diane Sayer as Barbara Wells

Davey Davison as Tally Raymond

Baynes Barron as Sgt. Mack Clyde

Ellen Corby as Mrs. Kroll

Russ Bender as Dr. Clarence Sanford

Jeanne Bates as Clara Thomas

Mimi Dillard as Thelma

Selette Cole as Helen Lawson

Michael Ryan as Detective Mel Posner

Wally Campo as Eggerton

Byron Morrow as Dr. Morton

John Yates as Intern

James B. Sikking as Police Sketch Artist

Robert Cranford as Jack Rosten

Fred Aldrich as Apartment House Manager (uncredited)

Benjie Bancroft as Police Officer (uncredited)

Fred Fisher as Detective (uncredited)

Kenner G. Kemp as Detective (uncredited)

Victor Masi as Attendant (uncredited)