As business propositions go, Captain America's shouldn't really have worked, but the Grafton Street institution is heading for its 30th birthday. In that time it has seen off countless other burger joints, the latest being the much-hyped Dublin branch of the international chain Planet Hollywood.

When a very young Mark Kavanagh opened his restaurant in 1971, he was introducing such exotica as Hawaiian burgers and desserts such as sticky mudslides and banana daiquiris to the longhaired, cheesecloth wearing trendies of the time.

One of the first hurdles was the location. First-floor restaurants rarely work and not only is Captain A's, as it is fondly known, up a flight of stairs, those stairs are notoriously steep and narrow. It did initially have the benefit of a reasonable ground-floor presence, as its entrance was also an entrance to one of Dublin's first shopping arcades, but over the years that went and the current entrance is no larger than a regular door.

Still, on a Saturday night the queue for a table winds down the stairs and out that door.

While up the road on Stephen's Green, burgers in Planet Hollywood start at £6.50, in Captain America's the basic burger costs £4.95. The current menu would be instantly recognisable to its first customers, as would the 200-seat restaurant's basic decor. There have been few changes.

Mark Kavanagh, now a major property developer with Hardwicke, sold the restaurant in 1993 to a company headed by another property developer, Paddy McKillen.

Ronnie Delaney is the hands-on MD of the current operation, while Paddy is known for his other business interests including the Jervis Centre. "It probably sounds corny," says Ronnie Delaney, "but when Mark came to sell, he didn't decide on the new owners strictly on the basis of price. When he was selling it was important to him that it was bought by someone who knew the place and wanted to continue it pretty much as it had always been."

Mr Kavanagh's own circle of friends played a key role in the success of the restaurant in the beginning.

Chris de Burgh famously busked there to earn pocket money for college, while others, such as the members of Horslips and Mr Kavanagh's racing driving friends, were regulars. Despite the proliferation of restaurants in the city, it's still a magnet for celebrities. It has been a regular hang out for home-grown girl and boy bands Bewitched and OTT, and recent visiting celebrities include Brad Pitt, who signed a t-shirt to add to the growing collection of memorabilia.

"We've been updating our memorabilia," says Mr Delaney who is the son of Irish Olympian Ronnie Delaney. "We've put together a huge collection of contemporary stuff from Naomi Campbell's bodice to Debbie Harry's shoes, usually by being the highest bidders at charity auctions."

When Captain A's first opened, its walls were covered with scenes of New York skylines and baseball collectibles. That has been changing slowly over the years with the new, more personality driven memorabilia taking over.

He says the restaurant has customers who have been coming since the very beginning and that they like the familiarity of the menu and the surroundings.

"It's a nostalgic thing for a lot of forty-somethings," he says. "We've had people in here who point to the table that they got engaged at 20 years ago or where they used to go to when they were students."

The student market is still very important to the business and to encourage them in, there is still the happy hour with cocktails costing £2.50.

Families are actively encouraged, especially on Sundays when a clown goes from table to table giving away balloons and T-shirts.

There is planning permission to add another floor to the Grafton Street premises which would make room for 150 more customers and Mr Delaney hopes that work will start sometime in the next year.

Its owners have thought about franchising the business or opening up in other Irish cities but for the moment have decided to concentrate on the flagship restaurant.

Just as Planet Hollywood looks set to close this summer, another competitor for much the same market will open. The American concept restaurant and bar, TGI Friday's, is opening on Stephen's Green in the old Chicago Pizza Pie premises.

"Competition has always been good for us," says Mr Delaney, "I don't really see that changing no matter who opens up."