The Hostel director told Metro that he was traumatised when he first saw Ridley Scott's 1979 science fiction film.
Roth said: "I saw Alien when I was 8 years old. To me, it was like a combination of Jaws and Star Wars and that's the movie that made me want to be a director.
"It traumatised me. I actually threw up I was so nervous after I saw it but that's like the highest compliment you can give a horror film."
"Then, when I was 12, I saw Evil Dead and that movie traumatised me too, but I also discovered that a 21-year-old [Sam Raimi] directed it, that you can go off in the woods with your friends and for not much money make a classic."
Roth, who produced The Last Exorcism, confirmed that the had seen William Friedkin's 1973 horror classic The Exorcist at an 'inappropriately young age'.
"Of course," said Roth. "And The Exorcist felt so real. I'd never seen anything that horrifying. It scared me for years, I had nightmares for years as a child and had always wanted to be involved in an exorcism movie."
> Q&A: Eli Roth and the 'Last Exorcism' gang