by Steve Ryfle Ever hear the story about the struggling writer who was so obsessed with Keanu Reeves that he paid a plastic surgeon $3,000 to make his chin and nose look like the "Matrix" dude? Or the honors student who flunked out of high school after he began spending too much time talking to fellow Ashlee Simpson fans in internet chat rooms? How about the woman who sent 6,000 fan letters to Michael J. Fox?

It's no big secret that America is obsessed with fame, and you don't need to read the supermarket tabs or watch "Access Hollywood" habitually to know that celebrities are part of our cultural landscape. For the most part, fandom appears to be a positive influence, a diversionary hobby if not taken too seriously.

But for some people, healthy admiration of a favorite star can turn into a sick obsession. And in extreme cases, fans cross the line and enter the frightening realm of stalkerdom.

In 2003, psychologists at the University of Florida and Southern Illinois University conducted a study on obsessive fans and concluded that about one-third of Americans suffer from Celebrity Worship Syndrome. The study divided fans into three categories. This first, comprising about 20 percent of the population, follows celebrity news for social purposes. The second, about 10 percent of the population, develops an "intense" relationship with a star, such as the belief that the fan and star have some special bond.

The third and scariest group, roughly one percent of the population, display "borderline pathological" behavior, and are willing to hurt themselves or other people in the name of a star. When asked if they would do something illegal for their favorite celebrity, most of these people said yes, and some even said they were prepared to die for their idol.

"Just worshipping a celebrity does not make you dysfunctional," said Dr. James Houran, one of the authors of the study. "But it does put you at risk of being so. There is this progression of behaviors, and if you start, we don't know what's going to stop you."

This "progression of behaviors" can begin in rather benign, if bizarre ways. Katie Becker of New York claims to have spent much of her income over the past few decades traveling the world to attend performances by Elton John. Some fans spend countless hours on the internet discussing the famous object of their affections (just check out the Michael Jackson newsgroups).

But these are harmless diversions compared to the extreme measures taken by a few fans, like permanently altering their appearances to resemble their favorite stars. In 2004, People magazine profiled a half-dozen fans who went under the knife to do just that. A 37-year-old woman, inspired by J-Lo's fab booty, paid $7,000 for "gluteal augmentation" (a fancy name for butt implants). A 20-year-old man paid $8,500 for a nose job and new chin dimple to make him look like John Travolta (that's a new one--wanting to look like somebody 30 years older). A 28-year-old woman spent $10,000 to get boobs like Britney Spears. And two 21-year-old identical twin brothers underwent nose jobs, chin implants, gum lifts, dental veneers and jaw implants (whew!) to make them look like Brad Pitt. And these people are just the tip of the silicone iceberg -- remember MTV's "I Want a Famous Face," with its parade of fans asking for breasts like Demi Moore's?

But none of this is as terrifying as when a fan becomes delusional and filled with irrational rage, love or other emotion toward a celebrity, and acts upon it. Fans who cross the line and threaten to put a celebrity in danger -- or worse, actually cause physical or other harm -- tend to suffer from deep psychological disorders, but they've been characterized by the media-at-large as little more than crazy stalkers.

We've heard the stories. A woman was arrested for breaking into Brad Pitt's home and sleeping in his bed; police found a book on witchcraft and a foot-long safety pin in her possession. She was sentenced to three years' probation and psychological counseling. A man was sentenced to 25 years in jail for stalking Steven Spielberg; he was found outside the director's house with a "rape kit" (duct tape, handcuffs, a utility knife). A woman was arrested after sending Michael J. Fox up to 15 letters a day, some of which contained rabbit droppings, and threatening to kill Fox's pregnant wife. A man was arrested for repeatedly breaking into Madonna's house and threatening to slice her throat if she didn't marry him.

The most horrific cases are well known: John Hinckley's obsession with Jodie Foster led to a presidential assassination attempt, while "My Sister Sam" star Rebecca Schaeffer was gunned down in her doorway by a fan. John Lennon was shot dead outside his New York apartment on 8 December 1980 by obsessed fan Mark Chapman.

And there are dozens more stories like these. Nicole Kidman, Will Smith and Jada Pinkett, David Spade, Katie Holmes, Meg Ryan, and Jennifer Love Hewitt have all fended off stalkers. And it's not just A-list Hollywood stars who attract such an unwanted gaze. In Britain, septuagenarian comedian Ken Dodd was pursued by a woman who sent him lewd photographs and a perfumed dead rat, then tried to burn down his house.

Halle Berry has jokingly said a celebrity hasn't made it until they've got their own stalker. Some stars spend hundreds of thousands of dollars on bodyguards and security systems to shield them from the threat. Fortunately, though, most fans don't take such extreme measures as stalking, or changing their face to look like Colin Farrell, for that matter.