This was the highest-grossing movie of 1987 in the United States.
During the two week rehearsal period before filming began, then-bachelors Tom Selleck and Steve Guttenberg took the long-married Ted Danson out on the town with them, visiting a few Toronto night clubs, bars, and restaurants, to rekindle the feeling of bachelorhood they had to project in the film. The three caused a lot of excitement among the public whenever they went out to party.
When Jack's mother comes to visit Mary (Lisa Blair), you can see in the background what appeared to be a little boy standing in a doorway. There is a rumor that this is the ghost of a little boy who died in the apartment in which the film was shot. This rumor is false, as the interiors were all shot on a soundstage in a movie studio. The "ghost" is actually a cardboard cut-out of Jack wearing a tuxedo. This prop appeared later in the movie, when Mary's mother comes to collect her.
Director Leonard Nimoy had some arguments and differences on the set with the lead actors. According to Steve Guttenberg, Tom Selleck and Ted Danson were used to being the bosses on their own television shows, but soon learned that the real boss in charge was Nimoy. Guttenberg said, "Leonard was a good director, and being an actor, he knew the problems actors face, although sometimes I think he forgot."
The Pampers company paid $50,000 for their brand of diapers to be used in the film.
Leonard Nimoy: (in voice only) the (face unseen) doorman opening the car doors for party goers just after Leonard Nimoy's director credit Saying: "Good evening" and "yes, ma'am"