An Adelaide bookshop owner has been "gently raided" by police for selling copies of the cult novel, American Psycho that were not plastic-wrapped.

The novel, by American author Bret Easton Ellis, has been classified R18 under national censorship legislation since its release in 1991, requiring it to be sold in plastic and only to those aged over 18.

It is a satirical book depicting a psychotic high-flying Wall Street worker in an era of "greedy" America and includes a number of very violent and graphically shocking passages.

Imprints Booksellers co-owner Jason Lake said previous editions had always been plastic-wrapped but the most recent edition was a Picador Classic with an introduction by famous Scottish author, Irvine Welsh, and it did not come plastic-wrapped.

"We just assumed the classification has been lifted," he said.

"I'd actually always suspected a ploy by publishers to keep it in plastic longer because it makes it stand out on the shelf.

"It's the only book on our shelf that we ever have with a plastic wrapper."

Mr Lake said the police were very gentle when they arrived and asked that the book be removed from the shelf.

He said the raid occurred because somebody complained to police after reading in a weekend newspaper column that the book was being sold by bookshops without plastic wrapping.

"I had a phone call from a lady on Tuesday who was quite aggressive and questioned why we were selling this classified product out of its wrapper," he said.

"My defence was it came to us like this. There's no way I would have removed the wrapping."

Mr Lake said modern crime fiction had come a long way since 1991 and there were now many books with graphic, sexual, physical violence depicted on their pages "available for anyone to purchase".

"This is not something that stands alone any more. It's all a bit silly," he said.

A police spokesperson confirmed they received a complaint regarding the novel.

American Psycho, by Bret Easton Ellis, was first released in 1991. ( Supplied )

"Police spoke with bookstore staff, who were very co-operative, and the matter was resolved to the satisfaction of police," she said.

"There is no suggestion the book has been on public display."

Mr Lake said the publishers had been made aware that the classification had not been lifted.

He joked that the book should be banned, not for its shocking content, but for "its quality of writing".

"It's not a great book at all, but it's a work of satire for goodness sake," he said.

"It was a comment on that period in America, the whole 'greed is good' era.

"It was a comment on the Masters of the Universe on Wall Street that were ruining the world.

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

The ABC has contacted Australian Classification for comment.