Censorship has proved to be alive and well after an Adelaide bookstore was raided by police for selling unwrapped copies of the cult novel American Psycho.

Jason Lake, a co-owner of Imprints Booksellers, says police asked him to remove the book on Friday based on a complaint.

"It was very gentle and polite ... I just think it's ludicrous that this person complained about the book," he said.

"In this liberal society, people should be free to read what they want."

American Psycho is classified as R18 under national censorship legislation, which means it can only be sold in plastic wrapping to people aged 18 and over.

Mr Lake said he had been selling the unwrapped edition since March.

"That's the way we received it from the publisher ... we just assumed that the classification had been lifted," he said.

Comment has been sought from police.