Adapted by William Peter Blatty from his own 1971 novel, the film was a huge international hit, the most successful horror film ever. It was nominated for ten Academy Awards (won two) and also won four Golden Globes. For its time the film had a number of graphic and disturbing effects. Blatty claims the plot is based on a true story (though this has often been used as a promotional gimmick for horror films).
A young girl named Regan living in Georgetown, D.C becomes possessed by the demon Pazuzu and undergoes a series of physical changes, as well as gaining certain malevolent powers. Chris MacNeil, Regan's mother, failed by medicine, turns to religion -- the girl is examined by a priest, Father Damien Karras, who is convinced of the diabolical nature of the case and turns to a second priest, Father Lankester Merrin, to perform an exorcism.
When the film was released into theaters, there were numerous reports of individuals screaming in terror and passing out. One man actually passed out and broke his chin on the seat back in front of him. He sued the production studio claiming he was "mentally tortured" by the subliminal images in the film, and they settled out of court for an undiclosed amount of money.
Adjusted for inflation, The Exorcist is the highest-grossing R rated film in history. Fourteen year old star (and Golden Globe winner) Linda Blair was accompanied by a bodyguard for six months after the film's release because the production studio received over 5,000 threats against her life. Televangelist Pat Robertson has decreed that the original film reels for the movie have "a demon trapped within them." (He was speaking literally.)
There were two poorly-received sequels and innumerable rip-offs (the popularity of The Exorcist inspired another Satanically-themed franchise, The Omen). A fourth film in the series is scheduled for release in 2004. A number of tales have also arisen from the making of the film, regarding accidents and deaths amongst the cast and crew.
Before The Exorcist was a movie, it was a novel based on the real life exorcism of an adolescent boy that took place between January and April of 1949. News of the boy's exorcism was published in the Washington Post on August 20, 1949, where it came to the attention of Blatty, then a student at Georgetown University.