The time of their lives: A star of stage and screen

When Dirty Dancing opened in New York on 17 August 1987, its screenwriter, Eleanor Bergstein, turned up to make sure there was at least one person in the audience. In fact, so convinced was Bergstein that the independent film, made with a budget of just $5m (£2.5m), was going to be a complete flop, that she went to every screening for five days. But then, at a cinema on 84th Street, her husband pointed something out to her - the girls sitting in the front row knew all the words.

"Do you know what that means?" he said. "It means that it's only the fifth day, and they must already have seen it enough times to know the words by heart."

A huge, stinking hit was born. Dirty Dancing went on to make $170m worldwide, became the first video to sell 100 million copies, and has since been adapted into a stage play-cum-musical that is sold out for months and took £10m at the box office before it even opened in the West End. And tomorrow, almost two decades after its first screening, a digitally re-mastered version of the movie will return to cinemas - just in time for Valentine's Day.

The numbers, though, are only half the story. Dirty Dancing has become a shared rite of passage for every generation of teenage girls since its release, just as it was for those first devotees at the front of the 84th Street cinema. Its music has been the soundtrack to a million crushes. And its one-liners - "nobody puts Baby in a corner"; "spaghetti arms"; "I carried a watermelon" - so often repeated that they became unassailable totems of adolescent pop culture. Even the laughable 2004 sequel, Dirty Dancing: Havana Nights, could not dent its appeal.

Which is surprising, given that the original Dirty Dancing is a distinctly middling film. Its plot surrounds Frances "Baby" Houseman (Jennifer Grey), the youngest member of an affluent Jewish family from New York, who are holidaying at Kellerman's, (a sort of upmarket Butlin's in the Catskill Mountains) in the summer of 1963. There she meets Johnny Castle (Patrick Swayze) - a dance instructor from the wrong side of the tracks - and his dance partner Penny.

Baby soon finds out that, after dark, these lithe folk are getting up to all sorts of naughty terpsichoreanism - or dirty dancing - in the staff quarters. She also discovers that Penny is pregnant and wants an abortion. The only problem is Penny and Johnny are due to perform a Mambo on the only day the doctor can carry out the operation. What's more, the procedure costs $250. So, Baby asks her father for the money. And then she learns to dance with Johnny so that she can fill in for Penny. And then Johnny and Baby fall in love and have sex and Baby's father finds out and no one puts Baby in the corner and, oh, I've had the time of my life. On its release, Roger Ebert, the Chicago Sun-Times's film critic, noted in his one-star review that although "Swayze is a great dancer, and Grey, who is appealing, is also a great dancer ... the movie plays like one sad compromise". Twenty years hasn't dimmed the critics' derision. Nev Pierce, editor of TotalFilm magazine, leads the chorus of disapproval: "It's one of those 'empowering' films I can't abide. It blighted my teenage years and continues to blight me now. It has that pseudo-liberal tinge which is about youngsters kicking out and doing what they want. In this case, doing what they want seems to be dancing a lot and having abortions."

But what do the critics know? This film, seldom cited as a masterpiece of alternative cinema, has always been carried on the shoulders of its messianic female fans. The reason the movie sold 100 million videos before any other is because it is the sort of film - think Point Break or Star Wars for boys - that is watched again and again.

Indeed, out of the dozens of women The Independent surveyed for this piece, almost all admitted to watching Dirty Dancing at least 10 times in their life. These are women who are otherwise sane - who hold down nice, middle-class jobs as lawyers and stockbrokers and doctors - but over whom this one film holds extraordinary power. Why?

"I think the secret of the film is that it ends where it does," said Delia Williams, 26, a trainee barrister. "We all know Johnny and Baby won't last. But that's fine. Girls like it when something comes full circle and their Dad finally realises they are not such a bad kid ... When Dr Houseman [Baby's father] turns to Baby and says, 'You looked wonderful up there', we all tear our hair out and cry tears of joy because that's all we want - for Daddy to say he's proud. We're very shallow."

Claudia Winkelman, a columnist for The Independent, and, born in 1972, one of the first generation of teenagers to fall in love with Dirty Dancing, has a simpler theory. "I used to watch it a lot," she said.

"What I loved about Jennifer Grey was she wasn't drop-dead gorgeous. And she has no makeover. She's still wearing a nylon pink thing at the end and hanging out with her dull family.

"It's a seminal film, just as Top Gun is a great film, and The Breakfast Club is a great film. People talk about Citizen Kane, but they're just trying to show off. Everyone knows, deep down, that Dirty Dancing is the greatest film ever made.

" It's formulaic, but it's a good formula: gawky girl falls in love with cool guy. Cool guy falls for gawky girl. It's cute."

For Polly Perkins, 26, now a vet, it was the fabric of the film that was so appealing. "All girls (especially when they were 12) longed for a Johnny and Baby holiday romance at a place where their parents would be so occupied with Lambada classes that they could sneak off to the 9th hole unnoticed. We also wanted to impress the cool kids with our spellbinding dance moves, which Baby gets to do... If Kellerman's really existed, I'd still book it in a flash."

Fans can espouse any number of strong theories about why the film holds such unique appeal. But is it actually the movie itself that keeps the girls coming back for more? Or is there something more interesting at work in the cult of Dirty Dancing?

The West End production - currently selling out the Aldwych Theatre - holds some clues. Apart from a weird additional storyline focusing on the American civil rights movement, the stage play is more or less a scene by scene (sometimes action by action) remake of the film. No effort has been made to turn Dirty Dancing: The Classic Story on Stage into a theatre play. Instead, it looks like a bunch of good-looking friends have got together to act out their favourite bits from a film.

Still, the producers knew what they were doing. Dirty Dancing has been one of the greatest successes in the West End's history. And, at tonight's performance - packed to the rafters with women of every age, reluctant male partners and young gay couples - the audience know they are going to have a good time before the curtain goes up. They cheer every line. They coo at appropriate moments. They whoop at the final number. It comes as no surprise to discover that, in the past three months, the Aldwych Theatre has become a top destination for hen parties.

In the foyer, meanwhile, the merchandise people not only sell Kellerman's sweatshirts and Dirty Dancing T-Shirts, but items with all your favourite lines. Want a pink "I carried a watermelon" bag? No problem. A "nobody puts baby in a corner" bib? Roll on up. It tells you one, important thing about the whole Dirty Dancing bandwagon - no one watches it for the story. At least, they don't any more. It has become a cult, a fetish, a participation event - a girl's night out. Anything but a film.

Bella Christian, 30, a City fund manager, certainly thinks so. "There was a time in my teens," she recalled, "where we communicated almost exclusively in Dirty Dancing lines. If you made a fool of yourself in front of a boy, for instance, it was 'I carried a watermelon'. That was how important it was to us."

Is it still important to teenagers? "Yes," says Sophie Hart-Walsh, 19. "I was ordered by my best friend to watch it, because she said I couldn't do anything until I had. It was this rite of passage - like Ferris Bueller's Day Off and The Breakfast Club. Actually, I didn't like it all that much."

She is not the only one. Jo Elvin, editor of Glamour magazine, remembers taking her boyfriend to see the film at a drive-in in Australia, and leaving halfway through. "I've often wondered," she said, "whether I'm the only woman in the world who thinks this film is just awful and always have. The fact that she's called Baby really irritated me from the start."

So, Dirty Dancing may not be loved by all of womankind, but its constituency is large enough to support two decades of video and DVD sales and spawn a West End hit. Right at the heart of its appeal is the in-built clubbiness that comes with cult movies (one journalist admits to having felt like "an alien" among her peers for not liking the film). The phenomenon shows no signs of slowing down, much to the exasperation of its star. "This," said Swayze earlier in the year, "is the movie that will not die".