Trivia

Warner Brothers sued the Italian production company behind Beyond the Door (1974) for what they considered to be a blatant rip-off of The Exorcist (1973). The case was settled in Warner Brothers' favor with the Italians forced to pay an undisclosed fee.

To drum up publicity for the film, the director hired actors to faint in theaters that showed the film, and also had ambulances parked outside the theaters. It worked, becoming a runaway hit in its native country.

Juliet Mills said she hated wearing the special prosthetic "possession" make up because it took a couple of hours to put on and another hour to come off. They also had to take it off very slowly or it would take her skin off.

During a 2005 interview Juliet Mills said the producers offered her a choice of either points in the movie or her salary. Her agents at the time, William Morris, said, "no, no, no, just get your money up front. You might never see the money with these Italians." So she took her salary. But then the film went on to become a massive success, which meant she lost out on earning a huge paycheck.

Mario Bava's Shock (1977) originally went by the title "Beyond the Door II" but had nothing to do with this film and was so named to cash in on the success of the original. The same is true of Beyond the Door III (1989).