James Caan's film debut.

Charles Laughton was director-writer Billy Wilder's first choice to play the character of Moustache in Irma la Douce (1963). Laughton, who had given an Oscar-nominated lead performance under Wilder's direction in Witness for the Prosecution, agreed to play the role, but died before principal photography commenced.

Jack Lemmon married actress Felicia Farr in Paris during this 1962 shoot.

Billy Wilder loved Marilyn Monroe's performance in Some Like It Hot and wanted her for this role but she died before production started.

Shirley MacLaine signed on without having read the script because she "believed in Wilder and Lemmon".

Shirley MacLaine was not happy with the script, and thought even less of the film after it was finished, calling it "crude and clumsy". She was surprised to get a Best Actress Oscar nomination out of it, saying "I would have been nonplussed had I won it."

According to Billy Wilder, Elizabeth Taylor was his first choice for the role of Irma but he didn't want to deal with the Elizabeth Taylor/Richard Burton affair going on at the time.

Although the film was based on a musical, Billy Wilder did it as a straight comedy because he didn't feel comfortable staging singing and dancing numbers.

Had director Billy Wilder succeeded in getting the cast he wanted, Charles Laughton would have played barkeeper Moustache and Marilyn Monroe would have played streetwalker Irma. Years earlier Laughton and Monroe did appear on screen together in Full House, with Monroe playing a streetwalker.

Several cars that traverse the streets of the set. A Renault Dauphine, A Citroen 2CV and at least one, possibly two Peugeot Sedans. At the end of the movie there are two Dauphines painted as police cars, too.

The original Broadway production of "Irma La Douce", the musical version, opened at the Plymouth Theater on September 29, 1960, ran for 524 performances and was nominated for the 1961 Tony Award for the Best Musical.

The pimps' union is called the "Mec's' (tough guy's) Paris Protective Association" (MPPA), which also stands for "Motion Picture Producers Association", an organization which had given director Billy Wilder some trouble.

The Seine was heavily polluted at the time of the shooting. For the scene where Lord X emerges from underwater Jack Lemmon had to be given a number of immunization shots, including tetanus, before entering the water. He later said it was the most disgusting thing he had ever had to do in a film.

The sprawling $350,000 Rue Casanova set took three months to build and included 48 buildings and three converging streets.

Throughout the film there are two small cars that go back and forth and are indeed the only two cars that appear in the film - one of the cars is a '53 Renault, the other seems to be a Peugeot.