Director Lawrence Kasdan's wife, Meg Kasdan, plays the airline stewardess flirting with Sam Weber at the beginning of the film. His two sons also have roles: Jon Kasdan plays Harold and Sarah's son in the bathtub, and Jake Kasdan plays the boy seeking Sam's autograph at the wake.
The main house in the film is in Beaufort, SC. It is the same house where The Great Santini (1979) was shot. Director Lawrence Kasdan liked "The Great Santini" so much that he decided to shoot his film in the same house.
The characters were based on people Lawrence Kasdan lived with in the Eugene V. Debs co-op in Ann Arbor, MI, while attending the University of Michigan. Co-ops are co-ed housing in which the residents share household duties like cooking. This explains why the characters are so comfortable sharing the house, cooking and are so attached to the Michigan football game.
Lawrence Kasdan wrote the parts of Karen and Sarah specifically for JoBeth Williams and Glenn Close respectively, however both actresses initially wanted to play the role of Meg as both felt that they better related to that character over the ones chosen by Kasdan.
At least twice during the movie we can see an octopus on a TV screen in the house. Of course an octopus has eight legs, and there are eight intertwined friends in the film (counting their friend Alex, who we barely see).