According to Dan Aykroyd, most of the production crew on Neighbors (1981) was on cocaine throughout filming, with the inevitable result that John Belushi was sucked back into an addiction he had been trying to quit. Belushi had been completely clean and sober during the making of Continental Divide (1981) which he shot just before Neighbors (1981).
Actress Blair Brown was cast in the co-starring lead role of Dr. Nell Porter because she resembled a young Katharine Hepburn.
The day that Lawrence Kasdan's agent put the script on the market, at least four studios instantly starting lobbying for it.
An early example of filmmakers putting "1138" in their films as an in-joke with George Lucas, referring to his first film THX-1138. The number can be seen on a taxi (with the camera lingering on the car a bit longer than necessary) as John Belushi leaves the train station in Chicago.
Third movie to be made by Steven Spielberg's production company "Amblin Productions" (now "Amblin Entertainment") with Spielberg being an executive producer on the film.