Le jour le plus longmet en vedette un grand casting comprenant John Wayne, Kenneth More, Richard Todd, Robert Mitchum, Richard Burton, Steve Forrest, Sean Connery, Henry Fonda, Red Buttons, Peter Lawford, Eddie Albert, Jeffrey Hunter, Stuart Whitman, Tom Tryon, Rod Steiger, Leo Genn, Gert Frobe, Irina Demick, Bourvil, Curt Jürgens, George Segal, Robert Wagner, Paul Anka et Arletty.