The movie was largely rushed into production. The original script was discarded and rewritten in one week, starting in March 1989. Principal photography had finished by the end of April, editing was done in May, and the movie was first screened at a film festival in July.
The original screenplay for the movie was written by producer Arthur Gorson and S.J. Smith. Monte Hellman disliked this screenplay however, and with Gorson's permission hired Rex Weiner to write a completely new screenplay. This was further revised by Hellman himself, his daughter Melissa Hellman, and Steven Gaydos. The rejected script by Gorson and Smith would subsequently form the basis of what eventually became Silent Night, Deadly Night 4: Initiation (1990).
The movie that the gas station employee is watching on the TV is 'The Terror' (1963), also directed by Monte Hellman (uncredited).
Director Monte Hellman attended a screening of the movie in July 2008 at the Alamo Drafthouse in Austin, Texas where he said he thought it was his best work, though not his best movie.
Dr. Newbury's assistant is played by Melissa Hellman, the daughter of director Monte Hellman. She also reportedly assisted her father with the final draft of the script.