The story that Billy Crystal tells about his "best day" of going to a Yankees game with his father is a true story from his childhood. He notes at one point that, "I still have the program." Not only does he really still have it, but he got Mickey Mantle to autograph it twice: once at the game that day and once again some 20 years later on a talk show they were both guests on.
As a rule, Jack Palance did not watch his own movies. Thus he did not see this movie until after he won the Oscar for it.
Daniel Stern declined the riding lessons offered for the movie in order to better convey his character's inexperience at horse riding.
Another true story from Billy Crystal's life portrayed in the movie is the wake-up call from his mother on his birthday. According to the DVD commentary, his mother would call him on his birthday at around 5 o'clock in the morning (the time he was born) and verbally re-enact the event over the phone. The rendition in the film is word-for-word the true story of Billy Crystal's birth.
Rick Moranis was cast alongside Billy Crystal and Bruno Kirby in a major role but left the project because his wife was diagnosed with cancer.