Want to Win an Oscar? Play a Crazy Chick.

If you want to know why Natalie Portman is a shoo-in for the Oscar, here's one answer. It's not just that she lost 20 pounds for the role, spent nearly a year practicing ballet, and delivered a performance that made us forget she was once the annoying Queen Amidala. It's because she played a crazy chick. Nina, Portman's overachieving ballerina, reads like a chapter from the Diagnostic and Statistical Manual of Mental Disorders. "There's the obsessive-compulsive. There's the paranoid. There's the borderline personality and schizophrenia," says Mark Heyman, one of the film's writers. Heyman didn't consult a doctor for any help with the character. He asked his mother. She's a therapist.

Mad Men might rule TV, but crazy chicks have conquered the big screen. Not only do actresses win Academy Awards by playing insane—just ask Kathy Bates (Misery), Nicole Kidman (The Hours), Angelina Jolie (Girl, Interrupted), or Jessica Lange (Blue Sky)—but movies featuring women beyond the verge play equally well with female and male audiences. Women, we're told, like crazy-chick flicks be-cause "they can console themselves, thinking, 'That woman is really attractive, but she's crazy, so I'm better than she is,'?" explains Sharon Packer, a New York psychiatrist who is writing about Black Swan for a medical journal. As for male audiences, Packer says, "I think it has to do with the Sir Lancelot feeling. Men might be more attracted to someone who has a degree of helplessness: being crazy is being helpless." Or maybe it's just that, as Black Swan fan Sean Kearney told us, "I can't think of a crazy girl who isn't hot." Kearney, 26, a videogame designer from Los Angeles, plans to be first in line when The Roommate opens Feb. 4. That film features Gossip Girl's Leighton Meester playing an undergrad who is so delusional, she dyes her hair the same color as her roommate, Sara (Minka Kelly), slips into bed with Sara's boyfriend, and then chases everyone around with a gun.

Actresses say they enjoy playing characters who've gone around the bend because it allows them a chance to stretch. "It's a lot of fun to act, I've got to say," says Barbara Hershey, who as the Black Swan matriarch plays "a mentally ill person taking care of a mentally ill person. It's a family of crazies!" Erika Christensen, who portrayed a crazy chick in 2002's Swimfan, says, "What appealed to me about the role was the fact that she was so different from me. She wasn't just someone where I could be playing myself." For The Roommate, Meester met with doctors who treated delusion. "It was really challenging," she says. "I tried to remain in the mood as much as possible." Halle Berry, who has been missing from the screen for a while, recently received a Golden Globe nomination for her stripper with multiple personalities in Frankie and Alice.

It goes without saying that, in real life, mental illness is a significant medical problem. Almost one in five Americans suffered some form of it in 2009, according to a study by the Substance Abuse and Mental Health Services Administration, and 11 million had a serious mental illness. Nonetheless, very few people seem to get offended when Hollywood uses mental illness as a plot point. While other Oscar contenders like The Social Network and The King's Speech have come under fire for questions about historical accuracy, the mental-health community hasn't voiced any qualms about Black Swan yet. "Does it do damage?" asks Packer, the New York psychiatrist. "I think it brings attention to how prevalent eating disorders are or how perfection can drive someone to the brink. The psychiatric disorders do the damage."

The crazy chick has been a theatrical staple since the days of classic Greek drama, when vengeful women like Medea tromped around the stage, murdering their children. Shakespeare's Ophelia went mad after her boyfriend killed her dad, and then handed out flowers like some proto-hippie before committing suicide. (Kate Winslet reprised the role in Kenneth Branagh's Hamlet, and Kidman pays homage in The Hours when her Virginia Woolf drowns, Ophelia-like.) The 1940s and '50s gave us the femmes fatales of film noir, with murderous women like Barbara Stanwyck in Double Indemnity. And who could ever forget Faye Dunaway in Mommie Dearest, her face smothered with cold cream, beating her daughter with a wire hanger?

But the actress who created the modern-day template is Glenn Close. "I'm not going to be ignored, Dan," Close warned Michael Douglas in Fatal Attraction, before cooking him dinner (rabbit, anyone?). Ever since then, actresses have been going nuts to play women who are off their rocker. For many actresses, playing crazy is good way to get noticed. Audiences didn't know who Sissy Spacek was until she was crowned at the prom with pig's blood in Carrie. Would Sharon Stone be a star if she hadn't wielded an ice pick and forgotten to wear her underwear in Basic Instinct? And before playing Winona Ryder's partner in crime in the loony bin in Girl, Interrupted, Jolie was just Jon Voight's daughter.

Not only do crazy chicks light up the silver screen, they invade our homes. (And, really, how can you describe Snooki without using the words "crazy chick"?) When Donald Trump invited Omarosa Manigault-Stallworth as a contestant on The Apprentice in 2004, she didn't just scheme, she came across as completely bonkers. The performance made her an overnight celebrity: talk-show appearances and other TV gigs followed. So did the imitators. There was Heidi Montag from The Hills, who is so out there, she reconstructed most of her face; Paula Abdul, who slurred her way through eight seasons of American Idol; and most of the cast of The Bachelor and The Real Housewives (we're talking about you, Danielle, from New Jersey). For these women, "crazy" is a backhanded compliment, a path on the road to fame. Two of the most famous examples—Britney Spears and Lindsay Lohan—wear the label "crazy chick" like a badge of honor, with the paparazzi trailing behind them to chronicle their every meltdown.

But for men, crazy doesn't carry the same cachet. We think of real-life terrors like Jared Lee Loughner or Jeffrey Dahmer. "Men go crazy all the time in the real world," says Heyman, the Black Swan screenwriter. The majority of insane male characters onscreen are violent sociopaths, explains Dr. Frederick Miller, founder of the Academy for Film and Psychiatry in Chicago, an organization of psychiatrists with an interest in film. "The most classic character is probably the Joker," he says. By contrast, mentally ill female characters tend to suffer from other personality disorders, he says, and are "women who desperately need the affection of a mate" (that is, until they stab their mate with a butcher knife).

These females aren't only more sympathetic than their male counterparts; they're a lot steamier. "The aggressive sexuality is part of the draw," says Swimfan's Christensen. In most crazy-chick flicks, the female protagonist doesn't just lose her mind; she loses her clothes. And sometimes she loses her sexual orientation as well. In Chloe, Amanda Seyfried stalks Julianne Moore and winds up in her bed. And most of the Internet buzz around Black Swan centers on the fantasy scene where Nina and her frenemy, Lily, stage a bedroom ballet. That's a major reason why 45 percent of Black Swan's audience is male, a fact that surprised even Nancy Utley, president of Fox Searchlight, which released the Darren Aronofsky film. When asked why men are so attracted to crazy chicks, Mila Kunis, who plays Lily, lets out a laugh. "I can give you a bulls--t answer," she says during the phone call. "I actually don't know. I think girls want stability and understanding, but I think..." She's interrupted by a noise in the background. "My father is changing a lightbulb. All my lights in my house went off at the same time. Dad, why are men attracted to crazy women?" She pauses. "He's thinking." She pauses again. "He won't say it. He censors himself around me. Dad, is it dirty?!"