Alex Comfort, 80, the British writer and physician who was best known as author of the best-selling 1972 book "The Joy of Sex," died March 26 at a nursing home in Oxfordshire. He had had a series of strokes.

With sales of 12 million copies and translations into two dozen languages, "The Joy of Sex" made Dr. Comfort an instant international celebrity. Although he had written 50 other books, ranging from a novel about the Roman emperor Nero to medical textbooks and volumes of poetry, the vast majority of readers remembered him only as the author of the book he advertised as a "gourmet guide to lovemaking." Originally it had been entitled "Cordon Bleu Sex," but the name was changed after the owners of the Cordon Bleu copyright objected.

"Before my book," Dr. Comfort observed, "writing about sex gave the impression of being written by non-playing coaches. Dear old Freud probably never witnessed an act of sex except in a mirror."

Although he considered himself first of all a poet and, in order after that, a physician, gerontologist, novelist, philosopher, anarchist and pacificist, Dr. Comfort was unconvincing in his argument that his work in other fields was more deserving of attention than his books about sex. "The grand old man of sex," he was called by London's Independent in a 1994 Sunday review. "In the Seventies, his name was synonymous with uninhibited hedonism and liberated sex."

Complete with drawings to illustrate various sexual activities, "The Joy of Sex" was modeled after a gourmet cookbook. "Chef-grade cooking doesn't happen naturally. . . . It's hard to make mayonnaise by trial and error, for instance. Cordon Bleu sex, as we define it, is exactly the same situation."

The book was arranged in three sections, "Starters," "Main Courses" and "Sauces and Pickles," and it was written in a lively and entertaining style that was often downright funny. "This must be one of the least inhibited books on sex ever written . . . its impact is straightforwardly healthy," The Washington Post's Book World said in a review.

In an obituary yesterday, the Guardian newspaper in London said, "Comfort couldn't have written bad English if he tried, and his erudition laced the text to make it worth reading, even if you weren't in search of the perfect orgasm. It was also good because of what it did for so many people's sex lives. Comfort gave his readers permission to regard sex as a normal occupation and a perfectly respectable interest."

In addition to discussing sexual techniques and positions, Dr. Comfort included such practical advice as getting rid of stains -- "either with a stiff brush, when the stain has dried, or with a dilute solution of sodium bicarbonate" -- and such warnings as, "Never fool around sexually with a vacuum cleaner." Open-air sex, he cautioned, could be risky. "Outdoor locations in wild areas are often flawed by vermin, ranging from ants and mosquitoes to rattlesnakes and officious cops."

In 1974, Dr. Comfort published a sequel, "More Joy of Sex," and in 1991 a third volume, "The New Joy of Sex."

He moved to the United States in the early 1970s and settled in California, where he was a lecturer in psychiatry at Stanford University and later a professor at the Neuropsychiatric Institute at the University of California at Berkeley.

For at least part of this period, he was at the Sandstone experimental sexual community in Topanga Canyon near Los Angeles, and he wrote about Sandstone in "More Joy of Sex."

The American author Gay Talese also visited Sandstone in the early 1970s, and he wrote about Dr. Comfort's presence there in his book "Thy Neighbor's Wife." "Often the nude biologist, Dr. Alex Comfort, brandishing a cigar, traipsed through the room between the prone bodies with the professional air of a lepidopterist strolling through the fields waving a butterfly net, or an ornithologist tracking along the surf a rare species of tern. A gray-haired, bespectacled owlish man with a well-preserved body, Dr. Comfort was unabashedly drawn to the sight of sexually engaged couples . . . and with the least amount of encouragement -- after he had deposited his cigar in a safe place -- he would join the friendly clutch of bodies and contribute to the merriment. . . . He was a rarity in the medical profession, one who brought a bedside manner to an orgy."

Alex Comfort was born in London and described himself during childhood as a "perfect little bastard."

At age 14, he tried to make gunpowder and in the process blew off the fingers of his left hand. He studied medicine at Trinity College, Cambridge, and received medical and surgery degrees at Cambridge University.

In 1944, he was licensed to practice by the Royal College of Physicians and accepted for membership in the Royal College of Surgeons.

He was a conscientious objector during World War II, and he continued anti-war activities after the war.

When he was jailed briefly in connection with anti-nuclear activity in 1961, he was said to have spent his time in prison teaching Irish revolutionary songs to Bertrand Russell, then 89.

During the 25 years from the end of World War II until 1970, Dr. Comfort was a lecturer in physiology at the London Hospital Medical College and later a specialist in gerontology at University College, London. In these years, he also wrote poetry, including contemplative poems about death, social histories, literary criticism, novels and a textbook on physiology and biography.

He wrote "The Joy of Sex," he told the London Sunday Telegraph, after "Somebody rang me to say that the London Hospital was not teaching sex properly and would I talk to them about it. So I spoke to the head of professional psychiatry and ended up agreeing to write a book myself."

It took him only two weeks to write the book, which he said was based on personal experience, reading and talking to people.

Shortly after it was published, his 29-year marriage to Ruth Muriel Harris ended in divorce, and he married his long-term mistress, Jane Henderson, a sociologist at the London School of Economics. She died in 1991.

After publication of "The Joy of Sex," Dr. Comfort continued to write on other topics. In "A Good Age" (1976), he offered practical advice on how to resist destructive pressures associated with aging. His last book and sixth volume of poetry, "Mikrokosmos," was published in 1994.

Survivors include a son from his first marriage, Nicholas Comfort, and three grandchildren.