Both William Peter Blatty and Paul Schrader were nearly thrown out of this film's premiere for loudly laughing during the screening.
Morgan Creek Productions fired Paul Schrader after he had submitted a completed movie, saying that he had given them "footage without any of the bloody violence the backers had wanted". He had already made it clear in interviews that he was making more of a psychological drama than an all-out gore-fest. He was fired and Renny Harlin was hired to re-shoot the movie. Almost 90% of the movie was re-shot and at least two characters have been dropped from Paul Schrader's version of the movie. Following the lackluster reception to Harlin's version, though, Schrader's version was finally released as Dominion: Prequel to the Exorcist (2005).
Nearly the entire cast (barring only Stellan Skarsgård) were either unavailable for the reshoots, or refusing to return out of loyalty to Paul Schrader.
When Morgan Creek hired Renny Harlin, he told them that Paul Schrader's version was complete crap and unsalvageable, and without any intention of actually signing onto the project, said that they'd be better off re-shooting from scratch. Much to his shock, James G. Robinson, the head of Morgan's Creek, agreed to this and offered Harlin an even bigger budget and paycheck than they had given Schrader. Harlin accepted the offer, and rewrote the screenplay alongside new writer Alexi Hawley.
William Peter Blatty said that watching this film was his "most humiliating professional experience."
Renny Harlin: [Finland] The character name of actor Roberto Davide is "Corporal Finn". The word "Finn" (pl. Finns) usually refers to a person from Finland.