From The Grindhouse Cinema Database
- Previously banned in the UK as part of the infamous "Video Nasty" list during the 1980s.
- Most of the torches for the dungeon scenes were lit by burning rubber cement
- According to Clint Howard, one night after shooting a scene he drove home while still wearing his bloody cadet outfit. He stopped at a light and noticed a woman staring at him from a nearby car, so he turned and smiled at her, and she responded by immediately locking all of her car's doors.
- The film earned over $400,000 the first week of its release, quite a large sum for its time, especially since it was only shown in Los Angeles and New York.
- One of the prosthetic heads was accidentally made too tough for the decapitation scene it was intended for, and when Clint Howard struck it with the sword to his embarrassment it merely bounced off. Frustrated, he found a large sledge hammer then took some time to practice swinging it around until the added weight made wielding the sword seem easy by comparison, and when the scene was shot again he finally took the head off.
- The title "Evilspeak" was derived from the phrase "computer-speak", a term used to describe the shorthand used by computer specialists for the otherwise complex. In the film the protagonist uses computers to summon evil spirits.
- According to Clint Howard and director 'Eric Weston (I)', the original cut of the film which he submitted to the ratings board contained even more footage than the current uncut DVD release, including more special effects, as well as extensions of the bathtub death scene and the cadet having his heart ripped out. But to date their labored efforts to find a copy of this version have proven futile, and they believe it is likely gone forever.
- Actor R.G. Armstrong was offered a choice between playing "Sarge" and Colonel Kincaid before assuming the role of Sarge.
- The production did some filming in a South Central church that had been condemned and scheduled to be torn down. When the aged minister saw that the crew were refurbishing the church, he didn't understand that this was "show business refurbishing" and that the church would ultimately be burned down, dropping down on his knees and thanking God. Nobody had the heart to tell him the truth.
- Clint Howard and Don Stark agreed not to socialize during filming so that they could maintain the hostility that existed between their characters.