This was the first film role for Stephen Root, then a stage actor. According to Root, he had been instructed by his agent not to let the casting directors know that he was inexperienced with film as an actor. Root's official debut was Crocodile Dundee II (1988), which had been released in theaters a month before this film, despite being shot a month after it.
This was George A. Romero's first studio film. However, the studio he was working with, Orion Pictures, had re-cut the film against Romero's wishes which contributed to the box office failure of the film. Afterwards, Romero went back to independent filmmaking until Stephen Kings Stark (1993) (also from Orion).
George A. Romero changed the ending at the insistence of Orion Pictures, his film's distributor. Romero's original ending was considerably less optimistic - it implied the film's evil forces were still at work. "I thought my ending played well, but I'd admit that the testing results were overwhelmingly in favor of the current version. To Orion's credit, they said - it's up to you, we'll release it either way. So I decided to go along and not fight it." He grinned. "But I'll always miss it."
One of the very few films depicting a quadriplegic having sex.
When Allan is experiencing his episodes of rage, his teeth change to resemble that of the monkey, primarily elongated canines.