Jerry Lewis was originally cast to play Al, but it was decided to let him act similar to his onstage comic persona and the character of Seymour was created for him.
Based on the popular radio program, Marie Wilson (Irma), Hans Conried (Prof. Kropotkin) and Gloria Gordon (Mrs. O'Reilly) reprise their radio roles. Conried replaced Felix Bressart who was cast in the film but died during production.
Alfred Newman's ubiquitous theme "Street Scene", closely associated with every New York-themed film produced at Fox during his tenure as musical director at that studio, turns up in the opening of this film and its sequel, My Friend Irma Goes West (1950).
According to a "Hollywood Reporter" news item, Jack Carson was originally slated to appear as "Al," but was unavailable. Marie Wilson created the role of "Irma" in the original CBS radio program "My Friend Irma ". Hans Conried and Gloria Gordon also re-created roles from the radio show. This film marked the feature film debut of the nightclub comedy team of Dean Martin and Jerry Lewis. According to Lewis, he quickly created the role of "Seymour" because he was worried that he'd be fired from the movie because he knew he couldn't play the straight role the studio wanted him to do. The "Variety" review stated that the "most notable value of 'Irma' is the introduction of two nitery comics," while the "New York Times " reviewer remarked on the "new mad comedian, Jerry Lewis . . . [who is] the funniest thing in this film." Modern sources add that Martin and Lewis received 10% of the film's budget as their salary. According to news items, writer-producer Arthur Kurlan sued for damages over the story rights to "My Friend Irma", "contending he had acquired all radio and TV rights to the 'My Sister Eileen' stories which CBS agreed to use . . . .[and] later told him they could use . . . without payment by changing the names of the principal characters and making them friends instead of sisters." The final outcome of the suit is not known. In 1950, Paramount released a sequel to this film titled My Friend Irma Goes West (1950) also starring Marie Wilson, Diana Lynn, Dean Martin and Jerry Lewis. (American Film Institute)