'I had the craziest dream last night, about a girl who was turned into a swan," Natalie Portman says, tremulously, in the early going of Black Swan.

But it can't possibly be as crazy as the Darren Aronofsky dream that follows for the next 100 minutes.

The director of The Wrestler has, with Portman as his fragile, fantastic collaborator, crafted a ballet movie that is also a psy-chological horror story and a scary reverie about obsession and paranoia. Black Swan opens the 19th Philadelphia Film Festival on Thursday night, reprises Saturday, and will be released locally on Dec. 10.

Wild and woolly, the movie is a breathtaking head trip that hails from a long tradition of backstage melodramas: 42nd Street, A Star Is Born, All About Eve, and, yes, that kitschy '90s relic, Showgirls.

That Aronofsky's Black Swan takes place in the rarefied spheres of the dance world - with its thoroughbred ballerinas, sinewy and high-strung - makes the nutty psychodrama somehow all the more intriguing.

Here is Nina (Portman), wrapped in a fluffy scarf, stepping from the subway and trooping off to rehearsals at Lincoln Center. Her whole life revolves around dance. There's a music-box ballerina in her bedroom - a bedroom still filled with the plush toys of her childhood, a bedroom in a cramped apartment she shares with her mother (Barbara Hershey), herself a dancer so many years before.

A new production of Swan Lake - stripped-down, primal, "real" - is on the season's slate, and the company's artistic director, Thomas Leroy (French actor Vincent Cassel), is looking for a new Odette/Odile to fill the pointe shoes left by his retiring prima ballerina, Beth MacIntyre (a just-this-side-of-camp Winona Ryder). Fiercely disciplined, Nina seems perfect for the part of the innocent, elegant White Swan, but Leroy expresses concerns that she doesn't have the sensuality, the slyness, to play her darker doppelganger.

Enter a new member to the troupe, Lilly (a cagey, sexy Mila Kunis), just in from San Francisco. She's as uninhibited and earthy as Nina is tamped-down and tightly wound. It's clear that Leroy sees star potential there.

Will Nina get the role? Will Lilly? Are Leroy's motives purely artistic? Are Lilly's overtures to Nina a guileless signal of friendship, or some sinister plot to usurp her position in the company?

Portman, in the role of her career, oozes anxiety and aching loneliness. Here is a young woman overwhelmed by her dreams and ambitions, sexually repressed, smothered by her mother, and in physical pain from the intense regimen of dance. But also in self-inflicted pain: She picks and claws her body apart like a dog gnashing at itself.

If you thought the bloody stuff Mickey Rourke's character subjected himself to in The Wrestler was tough (remember the staple gun?), Portman's Nina puts herself through even more torture and torment. Black Swan is, at times, exceedingly difficult to watch.

And then there are moments when you just can't help but laugh. And that seems fine.

Portman, shot mostly in closeup and mid-range, appears to be doing much of the dance work herself, and ably. Members of the Pennsylvania Ballet lend verisimilitude and artistry to the proceedings, and the staging of Swan Lake's climactic scenes, truly a transcendent fusion of music, dance, and cinema, is thrilling to behold.

Thrilling, indeed. And brazenly, beautifully crazy.