Dudley Moore was originally cast in the role that went to George Segal. He was fired by Barbra Streisand for not remembering his lines. These were the first symptoms of Progressive Supranuclear Palsy, a brain disorder that would later kill Moore. Conversely, in the earlier 10 (1979), Segal was replaced by Moore.
Barbra Streisand revealed in a 2014 interview that Lauren Bacall had trouble with scenes where her character was vulnerable, so to relax her, she stopped filming to help her through these moments; however, she secretly told cameramen to keep rolling, thereby enabling her later to choose the best take in which Bacall connected deeply with her emotions.
When Rose (Barbra Streisand) is putting things in Greg's (Jeff Bridges') house she puts up a picture of her parents. This picture is of Barbra Streisand's real father, and a picture of Lauren Bacall replaced Barbra's real mother.
On-location filming at Columbia University caused a campus-wide blackout one day.