Grant's arrest in Los Angeles (June 27, 1995), and his subsequent appearance on The Tonight Show starring Jay Leno, two days before the release of this movie, not only boosted the box-office take, despite unfavorable reviews, it also catapulted Leno's ratings over and above rival David Letterman's for the first time.
Robin Williams filmed his small supporting performance in this film at the same time Jumanji (1995) was being filmed.
After reading the script, Robin Williams originally wanted to play the Barney-like dinosaur. He later opted to play the doctor. Ironically, he played doctors-in other fields of medicine-for "Awakenings" (1990) and "Patch Adams" (1998). He also starred opposite Edward Norton's Barney-like performer in "Death to Smoochie" (2002).
Before Chris Columbus worked with Robin Williams on Mrs. Doubtfire (1993), he had seen him in comedy clubs in Los Angeles, where he was blown away by his energy. He thought he was one of the most impressive minds in comedy.