The original version of the movie was shot in 1981, and it clocked in at around 65 minutes. Additional scenes with students were filmed in 1982 to pad out the running time.
The actor who was hired to play Father Perkins didn't show up for the shoot, so director Richard W. Haines had to play the role.
The filmmakers were originally told they'd have two weeks to shoot at Mercy College, but the school cut their time by a week, so many members of the crew wound up sleeping in the classrooms to ensure the film was finished. When students returned to school, they were alarmed to find crew members cleaning up fake blood.
The opening scene in the asylum was shot in a then-recently closed psychiatric ward at Bellevue Hospital in New York.