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NC-17 movies used to sound as foreboding as the X variety — except they weren’t nearly as common.

Not so this year, when three NC-17 films will have been released by summer’s end — first “The Dreamers” in February, then “Young Adam” in April and finally “High Tension” in August.

Given the latest brouhaha over Janet Jackson's breast baring and increased sensitivity to indecent material, some contend that the NC-17 rating may become more common because it better reflects the level of sex and violence in films.

“NC-17 needs to be used,” said John Fithian, president of the National Association of Theater Owners (NATO) (search). “It’s an appropriate rating for certain films. The integrity of the ratings system as a whole depends on all the ratings being used.”

In recent years, NATO and the Directors Guild of America (search) have been lobbying the industry to make use of the rating when it’s warranted, according to Fithian. And it seems to be paying off.

“I think it’s a very important year,” he said. “If these three pictures are handled well and do as well as they’re expected to do, I think we’ll see a resumed usage of the rating in the future.”

"The Dreamers," a film by legendary filmmaker Bernardo Bertolucci (search) ("The Last Tango in Paris," "Stealing Beauty," "The Last Emperor") has made $2.5 million at the box office, which makes it the fifth-highest grossing NC-17 film of all time.

“Young Adam,” which stars heartthrob Ewan McGregor, opened April 16 and has only made $121,000 to date. "High Tension," set to open in August, is a French thriller labeled NC-17 because of violence.

Studios have long avoided releasing NC-17 movies, since the rating means no one 17 or under is allowed to see the film (translating into fewer box-office dollars) and carries connotations of sexual content that's so explicit it would make Howard Stern blush.

“It’s the kiss of death,” said Anderson Jones, a columnist for movie Web site Filmstew.com. “Generally, if you’re a studio going to release an NC-17 movie, you’re not interested in making money.”

NC-17 hasn’t been attached to any films with significant releases — in 100 or more theaters — for about six years, according to Fithian, so having three films with the rating in a period of six months is unusual. But it could mean there will be more in the future.

Still Paul Dergarabedian, president of Exhibitor Relations Co., a Los Angeles box-office tracking firm, said that major studios haven't been using the rating regularly yet.

“The reason you don’t see many is because by their very nature they restrict the audience,” he said.

In fact, studios will often go to great lengths to avoid NC-17 and get an R rating instead — demanding that directors clean up or cut certain scenes.

Filmmakers sometimes prefer the stronger rating over snipping scenes, but it means fewer viewers will see it.

“It is a positive thing in terms of the creative freedom it allows filmmakers, but it’s a double-edged sword because you’re hurting your chances for huge box-office success,” said Dergarabedian.

But directors behind content that warrants the rare rating aren’t usually interested in a blockbuster — they’re going for more of the art-house feel.

That was the case with Bertolucci and "The Dreamers," the story of an American student who is seduced by a brother and sister in Paris. The film received its NC-17 rating primarily for nudity, but Bertolucci's refusal to cut the offending material seemed to contribute to the movie's buzz, with write-ups in major newspapers across the nation.

"I am surprised that to show a naked body, which is the most natural and innocent thing, still provokes some kind of puritanical reaction," Bertolucci said in a published interview.

Fithian said the blackballing of NC-17 is based on myths about its effect — one being that theaters won’t show the restricted flicks and the other that television networks and print media won’t advertise them.

“With the right movies and the right markets, our members will play them,” he said. “And in our contact with newspapers, we’ve found they would run the ads on a case-by-case basis. ... There are very few blanket bans on NC-17s.”

But still, the stigma has stayed — to the point where flicks that some feel should have been NC-17, like “Y Tu Mama Tambien,” have hit theaters unrated instead.

Despite studios' reluctance to accept the tough rating, Dergarabedian said sometimes NC-17 might help more than it hurts by enticing curious viewers because of a certain “Je ne sais quoi” appeal it holds.

“There’s a prurient interest among a lot of people to see it,” Dergarabedian said. “That’s part of the mystique of the NC-17 film.”