It is said before the field trip that one of the group has not left the hospital in twelve years. As the story progresses, the viewer learns that Billy (Michael Keaton) has been there for a year and a half and Henry (Christopher Lloyd) for two. Later, Jack (Peter Boyle) visits his old office and most people remember him, implying he hasn't been gone for more than a few years. This leaves Albert (Stephen Furst) as the long-term patient, the only one of the group whose earlier life nothing is revealed about.
Billy (Michael Keaton) jokingly tells the shopkeeper that he and his group are a special combat unit with the US Marine Corps after some Libyan terrorists. This may be a reference to Back to the Future (1985), where Libyan terrorists were after Christopher Lloyd's character, Doc Brown.
First of two movies released in consecutive years where actor Michael Keaton played a psychologically disturbed character. The second film was 1990's Pacific Heights (1990) where Keaton played a psychotic tenant.
Some movie posters for this film featured a long blurb that read: "This morning they were playing ping-pong in the hospital rec room. Now they're lost in New York and framed for murder. This was never covered in group therapy. The Dream Team. Four guys on a field trip to reality".
The place where the hospital inmates went on a day trip to see a baseball game was the "Yankee Stadium". The venue was closed in 2008 and demolished in 2010. The site where the sports arena existed is now parklands.
At one point in the picture, Jack McDermott (Peter Boyle) says: "I was pulling down one hundred big ones a year when you Satan and were out chasing Daryl Hannah!". In the following year after this movie launched, Hannah co-starred with Dudley Moore in a psychiatric comedy of her own, 1990's Crazy People (1990).
The film's "Dream Team" title would become about three years after this picture debuted the nick-name for the US National Men's Olympic Basketball Team. The "Dream Team" name would continue to be permanently be associated with the basketball team but this film was first released before the nick-name for them was formed in 1992.
All three characters that Michael Keaton played in movies in 1989 were all 'B' names with first names beginning with that letter. They were Billy Caulfield in this film and Batman and Bruce Wayne in Batman (1989).