Jack Lemmon was almost killed in the manhole explosion scene. The blast was much stronger than anticipated, and instead of only lifting the manhole cover a few inches up and away from the hole, it threw it several feet into the air. A few seconds later, it falls hard in the ground, very close to Jack Lemmon's head. The actor was then hit in his left leg when the cover bounced, and although startled and in pain, he stayed in character. That shot was used in the final film.
The bases of the newly-begun World Trade Center towers, risen to 10 or so stories, are visible in the scenic view of Manhattan from the airplane. They are unmistakable because of their rusty red patina, which was still in place when the towers fell 32 years later.
Unlike many Neil Simon efforts, which were written as plays and then adapted into films, Simon wrote this directly for the screen when he realized that a play would have difficulty portraying the many different locations involved.
Many of the smaller supporting roles were cast with well-known comedians such as Anne Meara, Sandy Baron,Paula Prentiss, Paul Dooley, and Anthony Holland.
The first airport scene showing the Kellerman's departure was filmed at MacArthur Airport in Islip, Long Island.