 The inspiration for the book (published 1971) on which the movie was  based dates back to a real episode of exorcism that occurred in  1949. Writer William Blatty was at Georgetown University and had  read a Washington Post (20 August 1949) account by Bill Brinkley  ("Priest Frees Mt. Rainier Boy Reported Held In Devils Grip") of an  exorcism, involving a 13 year