On my first morning in Portland with Chuck Palahniuk, we visit his favourite shop, Lippman's gift store, where he buys 50 dark-brown plastic turds and several pink life-sized severed feet. As he is perusing the 'Fake Wounds' section, deciding whether to opt for the stick-on 'Slashed Wrists' or the stick-on 'Sliced Throats', the manager arrives with good news and bad news. 'We just received a new batch of vomit,' she says, 'but we still don't have the severed fingers.' Chuck looks perturbed. 'You know what?' he says. 'I'm gonna pass on the vomit. I think I might have overdone it with the vomit.'

After Chuck has racked up a couple of hundred dollars on his credit card on novelty items, we drive a few blocks to WalMart, where he buys 20 small cuddly creatures, kittens and puppies mainly, and a few rabbits and rodents. 'I try to avoid the white ones,' he says, discarding an albino gopher. 'They get dirty real quick.' I nod, distractedly, my thoughts suddenly hijacked by foul imaginings about the various heinous uses a character in a Chuck Palahniuk story might find for a pink fluffy gerbil.

This is not research, though, this is Chuck's way of saying thanks to his fan base. One of each will end up in an individually packaged gift box, alongside an individually penned letter from Chuck to each and every one of the faithful who have written to him. 'I've lost count of the times people have come up to me after an event and said, "Thanks for the fluffy toy, Chuck, my daughter loves it so much." People treasure the fluffy toys.'

Back in the pick-up, he tells me that each gift box is worth about $25. I do the math: a thousand boxes adds up to twenty five grand, not counting postage. That's a lot of money. 'It is,' he says, still smiling. 'But you know what? I have a lot of money.'

If I were to hazard a guess as to why Chuck Palahniuk has so much money, and such a devoted global fan base, I would say that it is mainly because he writes novels for the kind of people who don't normally read novels. His stories tend to be extreme, both in their subject matter and in their telling. Chuck is big on the neuroses of modern America: addiction, support groups, cults, plastic surgery, paranoia, New Age therapies, terrorism, eating disorders, terrifying terminal illnesses. He tackles these subjects head-on, without too much unnecessary scene setting or mood building.

'I like to cut to the chase,' he says. 'I try to tell a story the way someone would tell you a story in a bar, with the same kind of timing and pacing.' To this end, he listens a lot. While other writers might go to the library, Chuck goes to Starbucks. 'You hear the best stories from ordinary people. That sense of immediacy is more real to me than a lot of writerly, literary-type crafted stories. I want that immediacy when I read a novel,' he says, sounding evangelical. 'I don't want all that other extraneous stuff, all those abstract, chicken-shit descriptions.'

To this end, a Chuck Palahniuk novel reads like a film transcribed on to the page. In Survivor, a cult member devoted to mass suicide speaks his life story into the black box of the airliner he has hijacked; in Lullaby, a children's story spreads like a virus through America, causing those who hear it to die; in Fight Club, his best-known work, a man addicted to addiction self-help groups is mesmerised by a charismatic stranger who introduces him to an underground network of illegal bare-knuckle boxing, the first stage of his plan to wage war on capitalist America.

Chuck Palahniuk is one of the most popular novelists in the world. Put simply, his fiction hits a nerve with people whose lives - and desires and neuroses and pitch-black humour - go unrecorded by most writers of fiction.

'There are people out there who will not read books, but somehow they'll read my books. They serve them in a way most fiction doesn't. I give them a less filtered form of entertainment. I acknowledge some unacknowledged parts of our lives, which, as a culture, we don't tend to talk about.'

Chuck tells me that after Fight Club became a bestseller, his readings always attracted one or two serious young men who would ask him where they could find a fight club in their area. 'I always felt bad telling them that they didn't actually exist, that I made them up, but the fact they were looking for them somehow attested to the power of the fiction.' On his last reading tour, Chuck regularly caused people to pass out while reading 'Guts', a story about people masturbating underwater, which culminates in unforeseen and bloody consequences when one protagonist gets his insides entangled with the filter of a swimming pool. Nick Hornby, this ain't. 'Now, when I do readings,' he says, 'the stragglers come up to me and say, "I need to tell you a story I have never told anyone." And they nearly always tell me a horrific childhood sexual story. By reading 'Guts', I've shown them that you can use these awful things that happened to you rather than be used by them. Just telling the awful story is like a jumping-off point.'

Over lunch at the Multnomah Falls, a spectacular Oregon landmark, Chuck tells me about his new book, Haunted, a selection of interconnecting short stories - including 'Guts' - and odd, neurotic-sounding poems. In its formal experimentation, Haunted breaks new ground, and, one suspects, may test the patience of the Chuck fans who don't like reading any books but his. It concerns a group of would-be writers who come together to tell their stories, and, more pertinently, to avoid telling the bigger, darker collective story of the group. The bigger story emerges nonetheless and it is by turns nauseating, darkly funny and brutally graphic.

'The initial premise for the book was Edgar Allen Poe's short stories,' says Chuck, acknowledging an influence that few have picked up on. 'Poe was so good at writing stories that exploited the unspoken horrors of his day. He was obsessed with premature burial, for instance. I kept thinking, "If Poe were alive today, what would be the everyday horrors he would write about?"' He pauses to fork some seared salmon into his mouth. 'Plus, I had to write a food book. Every author has to eventually write a food book.'

Chuck's food book, needless to say, is not like anyone else's food book. It is, in almost every way imaginable, pretty unappetising. 'It's about the horrible things we do with food other than eating it,' he elaborates, 'just like the sex in my book Choke was about death rather than life. Every story contains food in some way, but is told by people trying to deny their hunger. That's the big concept.'

He seems like such a nice, well-balanced chap, I tell him, to have such peculiarly graphic fantasies, not at all the gleeful anarchist-come-nihilist described in book reviews. 'Well, Charlotte Brontë was probably called a nihilist and an anarchist,' he replies, sounding slightly pissed off that I have used the two words often thrown at him by reviewers who find his books adolescent and misanthropic. 'That is just lazy journalism. My books are always about somebody who is taken from aloneness and isolation - often elevated loneliness - to community. It may be a denigrated community that is filthy and poor, but they are not alone, they are with people. Typically, too, my characters make that Kierkegaardian leap of faith to commit themselves to one person. I write nothing,' he says without a trace of irony, 'but contemporary romances.'

Before he became a romantic novelist, Chuck Palahniuk worked at Freightliner for 13 years, fitting front axles to big trucks, then writing manuals telling people how to do the same. For a while, too, he tried his hand at journalism. Both 'closed him down'. A casual visit to a 'group awareness' seminar conducted by the Landmark Forum, an organisation that uses ideas based on controversial 'est' therapy, was, he says, his 'big epiphany moment'.

'I was 26 when I did the seminar, convinced the world was out to burn me at every turn. If it wasn't for that seminar, I wouldn't be a writer. They taught me to see how closed down I was, to face my fears.'

Armed with 'est' awareness, Chuck quit his job in journalism and set about confronting his fears big time. He was so worried about becoming poor and homeless, he went to work as a volunteer in a homeless shelter. 'You get to see how the homeless live, and you think, "Hey, it's not so bad. I could be a homeless person if I had to."' Then he confronted his fear of dying by working in a hospice for the terminally ill. 'By going to hospices, you get to see how people die. You see death unpacked into schedules and details and doctors' visits, and you suddenly think, "Hey, I could do this! This is easy!"'

I ask him if writing, too, is a way of confronting his primal fears. 'I don't think so,' he says, without a second thought. 'I mean, I enjoy it way too much.' His stories, though, however much they take on America's collective fears and neuroses, are, on some level, about his own fears and neuroses. 'Oh, definitely. If they are satires, it is usually me satirising myself, the traps I fell into, the self-help groups I attended. It's all me. I'm the guy who had the Ikea catalogue in my drawer at work.'

When he decided he wanted to be a writer, Chuck started attending a writer's workshop hosted by Tom Spanbauer, a local author, and one of the guiding lights of minimalist fiction, whom he now acknowledges as his mentor. On my second morning in Portland with Chuck Palahniuk I go with him to one of Tom's workshops. One person reads a fragment of their work in progress while the others listen intently, then Tom pours encouragement on the reader, and makes some suggestions. It is all very mutually affirming in that peculiarly American way that, like Oprah or the 12 Steps, suggests a world devoid of embarrassment. I'm not sure if this is a good or a bad thing.

The best bits by far are when Chuck chips in, offering suggestions which are always outrageous, as if he wants every one to go as far out in their fictions as he has in his. I remember something he said earlier. 'I set out to shock myself because if I can't shock myself, I'm not going to shock anyone else. Unless I feel I've gone a little too far, I'm not going to feel I went far enough.' Sadly, though, everyone here wants to be Raymond Carver, and no one wants, or dares, to be Chuck. As minimalists go, he is a one-off. For a start, he finds writing fun. Driving back across town, he says, 'Tom's books are beautiful and sensitive. But each one has to be an existential struggle and torture. I just refuse to write in that paradigm.'

Writing, then, has become not just a way for Chuck to confront his fears, but a means to escape into a world of play. In his books, he remakes the world as a darker, funnier, weirder and scarier place than it already is. Which, in his case, is no mean feat. When he was 18, Chuck's parents took him aside and told him the truth about his grandparents. This is how Chuck tells it in an essay called 'Consolation Prizes', from his collection, Nonfiction. 'My father was four in 1943 when he hid under the bed as his parents fought and his 12 brothers and sisters ran into the woods. Then his mother was dead, and his father stomped around the house looking for him, calling for him, still carrying the shotgun.'

How did he feel at that moment? 'I just thought, "Why didn't you tell me before?" All this time I thought they had died of rubella.' Did he never suspect that there was this dark family secret? 'Never. We always went back every summer to that old family house in Idaho where it had happened, so we spent every summer of our childhood sleeping in the murder room. How twisted is that?' he asks, proudly. 'My mother said, "I used to hate turning off the light and leaving you in there."'

Chuck says he had 'a regular tense American childhood'. He was raised a Catholic, but insists he and his siblings only went to church so 'my parents could have sex in other rooms apart from the bedroom'. Does he still believe in God? 'Well, I believe there's a divine something, but I believe we're not supposed to know it. There are too many things unexplained in the world for me to be a non-believer.'

In the summer of 1999, when Fight Club was turned into a critically acclaimed film starring Brad Pitt, Chuck learnt that his father had been murdered. The woman his father had just begun dating was being stalked by her husband, who had threatened to kill her and any man she befriended.

'My dad got killed at the end of May and the film came out in October,' Chuck says quietly. 'It was the best and worst you could perceive of. I remember being in the coroner's office alone, because none of my siblings would come, which was irritating, and I had to look at these photos with a sheet of paper over the top. My father's dead, burned body. The coroner pulled the sheet of paper across really slowly. It drove me crazy. I took his hand and moved it, and it was him. Unmistakably.'

Since then, Chuck has requested that Dale Shackelford, the man who murdered his father, receive the death penalty. Does he have any qualms about that decision? 'Well, I'm not sure it's a decision I would make now.' Does that mean yes, he has? 'Boy, let's see,' he says, sighing. 'No. I would still say, "Yeah, fry the man." The thing is, I'd be a lot more nervous about the fact that this man was still in the world. This is a guy whose ex-wife - the woman he killed and burned - was a lawyer that he met while in prison. She taught him the legal skills to write appeals, which he'll be writing for the rest of his life. So, it's kind of a non-issue.'

Last June, though, Shackelford had his first appeal turned down. 'This is a guy,' says Chuck, 'who said he'd buried anthrax bombs in Spokane and Seattle, and unless they released him, he would allow them to degrade until they exploded, killing thousands of people.' Phew, I say. 'It just goes on and on,' says Chuck, sighing some more.

Driving back into Portland, Chuck tells me that, back when he was a little boy, he chose St Lawrence as his Confirmation saint. 'The first investigative journalist. He investigated papal prefects in the Vatican who were stealing money. He got killed for it,' Chuck says, beaming. 'Barbecued alive on a big grill. Kind of scary, eh? It's like, we attach to these roles really young in life. You could say I'm always trying to get the story so I can tell it to other people. I really believe it's the moments we can't talk about that become the rest of our lives. It's the moments we cannot process by telling a story that destroy us in the end.'

· Haunted is published on 2 June by Jonathan Cape, £12.99. Visit Chuck's own website at www.chuckpalahniuk.net