The year was 1977 and I was 15, overwhelmed with the excitement and glamour of it all. I was sitting in the first Irish McDonald's on Grafton Street with my friends from school and eating an American hamburger for the first time in my life. Never mind that I had to pick off the tomato ketchup and pickle, neither of which I liked. This was American youth culture, as real as the Cokes we drank out of straws through plastic lids. We sat on shiny plastic seats and ogled a group of boys crammed around a plastic table next to us. We put our pennies together to see if we could afford that most exotic of items, a milkshake.

Fast-forward to 1982, when for a few penurious summer months I was working in the third McDonald's to open in Ireland, in Dun Laoghaire. Not so glamorous. Lots of mopping floors, getting sweaty in a nylon uniform, burning my hands toasting buns and shaking fries into boxes under hot lights. Putting gherkins as cold and damp as frogs on Big Macs and firing gobs of sauce from a sauce gun on to deep fried fillets of fish.

Now let's look into the future. It's 2000 and there are 75 McDonald's restaurants in Ireland employing 5,000 people. No, we aren't dreaming. This is for real. Currently there are 39 restaurants in the Republic (with 15 in the North), but McDonald's, which turns 21 this year, is aiming to virtually double that in fewer than two years.

"There's been a growth in the Irish economy and an increase in disposable income," says Andrew Corcoran, country manager for McDonald's in Ireland. "We were careful about opening in small towns initially. We thought the sales may not justify the investment. But our successes in Tralee, Navan and Monaghan have shown that we can do good business in Irish provincial towns." Later this month a drive-through McDonald's will open in Castlebar, and next month there will be a restaurant opening in Mallow and a drive-through in Roscrea.

In 1997 alone there were approximately 54 million customer visits in the Republic and the total turnover was £60.3 million. Yet McDonald's in Ireland is a mere drop in the ocean when you consider that worldwide there are over 23,132 McDonald's restaurants in 109 countries, supplying food to 38 million people daily.

What is the winning formula? And why is it working so well here? "Food, folks and fun," quips Andrew Corcoran. But really? "Tasty food, friendly service and a clean environment." But what do Irish people, specifically, like so much about McDonald's? "The average sales of our fries are, I think, the highest in Europe. Irish tastes in general mirror Northern European and American tastes, but the consumption of French fries in Ireland is particularly high."

Time to tackle the consumers at the coalface. The Grafton Street McDonald's is packed with students, families, and several groups of older women at lunchtime on Thursday. "It's mad," announces Tom (11), whose mother doesn't want him to give his real name. "The food is lovely." He has just eaten a cheeseburger and is finishing a strawberry milkshake. His brother Frank (13) prefers chicken Mcnuggets. "They taste great." Their mum sounds a note of caution. "It's not nutritious. They'll need another meal in an hour." Their dad chimes in: "It's novelty value, but it's just a snack. We'd have to go somewhere else for real food."

There are lots of facts and figures in the nutrition and healthy eating section of the McDonald's Fact Pack explaining that the food is good for you. "Only prime cuts of lean forequarter and flank are used for McDonald's 100 per cent pure Irish beef hamburger patties." As for the potatoes: "McDonald's only use the best quality grown potatoes for their French fries - Russian Burban, Pentland Dell and Shepody." Recent "nutritional developments" include the replacing of lard with "a smaller quantity of vegetable oil" in the buns.

In the last 18 months McDonald's has even introduced a vegetarian pattie in a bun: "It's an appeal to vegetarians, who are a small but growing sector of our society," explains Andrew Corcoran.

Nevertheless, the menu at McDonald's is not the sort of highfibre, crammed with fresh fruit and vegetables healthy diet that we currently accept as the best way to eat. "Fast food in general may be acceptable for occasional meals but would not be recommended as a regular eating option," says Vivienne Reid, senior dietitian at the department of preventive medicine at St Vincent's Hospital in Dublin. "A diet that has very little salad or vegetables and a high fat content is not good for anyone, and certainly not for children. You can eat convenient and healthy food at home, and make the most of the season's fresh produce."

On the other hand, "McDonald's fitted into a pre-existing pattern of fish-and-chip culture that was already established in Ireland before 1977," points out Jerry Boucher. "Irish people don't eat a lot of fresh fruit anyway." Mr Boucher, who hails from Hartford, Connecticut, is completing his Ph.D at TCD's department of sociology on Ireland's integration into the global economy. The biggest customers in McDonald's, says Andrew Corcoran, are mothers with groups of children under 12. "We're glad we have created the kind of atmosphere that attracts families," he says. "Parents like a clean, safe environment, where there is someone to help with the children, and where there is food that children like. Our birthday programme, happy meal programme and give-aways for children are all very popular." Meanwhile, the Ronald McDonald Children's Charities has given grants of $150 million.

Gerry Boland, co-ordinator of the Dublin Food Co-op (an organic wholefood co-op on Pearse Street), is critical of the approach McDonald's takes in attracting children. "Children are exploited by this tactic of making eating there a fun day out with Ronald McDonald and give-aways. Children are not the ones who should be making decisions about what they are eating."

He adds that the fast food McDonald's epitomises is "contrary to everything we in the food co-op are trying to promote. It is mass-produced, so it involves chemicals, pesticides and animal exploitation." He also criticises the McDonald's packaging. "We promote minimal packaging in line with strict environmental principles." He recalls picketing branches of McDonald's during the recent McLibel case, where two people in England distributed leaflets critical of McDonald's and were sued.

"The McLibel case didn't affect McDonald's in Ireland," says Andrew Corcoran. "Anyway, McDonald's won the case and the wording of the leaflet had to be changed. It had been full of incorrect statements about our environmental policies." McDonald's "does not purchase beef which threatens tropical rain forests anywhere in the world", says the Fact Pack. There is also a list of the recycled content of McDonald's packaging (napkins are 100 per cent recycled, other containers are 72 per cent). Andrew Corcoran adds that McDonald's employees do hourly "litter patrols" outside each restaurant.

As for suppliers, McDonald's are supplied and supported by 19 companies. "Wherever possible we use local produce," says Mr Corcoran. "Some things, due to the volume of the product we need, we can't get locally; for example, our buns. But we are looking at building an Irish bakery."

McDonald's has also been criticised for not recognising unions. The editor of the Socialist Worker, Kieran Allen, says: "It has a militant policy of keeping unions out. The employees are very controlled by management." Andrew Corcoran responds that there is no need for a union because "we liaise closely with our employees, we have rap sessions and day-to-day communications. One of our head franchisees is on the Joint Labour Committee. At McDonald's we value our people. We know it can be a tough job and they can be very busy. This is not just a trite corporate statement."

For a deconstruction of the fastfood phenomenon of which McDonald's is king, Kieran Allen recommends the work of the American sociologist, George Ritzer, who has written extensively on "McDonaldisation", the "dehumanisation and homogenisation" of our consumption patterns. "Eating is at the heart of most cultures and for many it is something on which much time, attention and money are lavished," says Ritzer in The McDonaldization Thesis (Sage Publications). "In attempting to alter the way people eat, McDonaldisation poses a profound threat to the entire cultural complex of many societies. It is little wonder that McDonald's and its many clones have become a focus of anti-Americanism. What is more surprising is that so many people in so many societies are so eager to embrace McDonald's and the process it epitomises."

But sociologist Gerry Boucher plays down any notion of McDonald's being part of a wave of American culture that is swamping Ireland. "Ireland is developing very quickly and is adapting to other cultures. But that doesn't mean Ireland is losing its cultural identity. In fact, the huge Irish diaspora has succeeded in introducing Irish culture all over the world, from the Guinness pub concept and Riverdance to Seamus Heaney and Boyzone."