Jerry Lewis had worked as an usher for Suzanne Pleshette's father Gene Pleshette at the Paramount Theater. When she auditioned, Lewis phoned Gene in disbelief.
Lewis says the word "Harry" 117 (and 1/2) times in the film.
In the scene in which the 1958 Los Angeles Dodgers are playing an exhibition game in Japan, the actual ball field is the venerable first Wrigley Field, located in Los Angeles, at Avalon Blvd. and 42nd Place, from 1925 -69. The stadium was the first of its name (sorry, Chicago) and was used mainly for minor-league baseball games. Wrigley Field, Los Angeles also masqueraded as Yankee Stadium in Vainqueur du destin (1942).