The Exorcist. 1973. (2000 extended version)
When 12 year old Regan MacNeill becomes possessed by a demon her mum seeks out help from two priests to save her daughter's soul and life.
Thank you William Peter Blatty for the book that rocked our imagination and thank you to William Friedkin for making us shit ourselves, with great acting, special effects and make-up still makes this film scary 47 years on. Even though some scenes were trimmed down a bit and more added with blink and miss it moments, I still cringe with carotid angiography operation scene.