The second-most-influential psychotherapist of the twentieth century, by the reckoning of the American Psychological Association, turned ninety last month. His name is Albert Ellis, and, in case you didn’t know, he is the founder of Rational-Emotive Behavior Therapy, or rebt, and the author of more than seventy books, including “Sex Without Guilt,” “Sex and the Liberated Man,” “The Case for Promiscuity,” and “How to Stubbornly Refuse to Make Yourself Miserable About Anything—Yes, Anything!” Ellis started out as a psychoanalyst, in 1947, but soon decided that exploring his patients’ childhood traumas had “nothing to do with the price of spinach.” By the mid-fifties, he had devised his own method, based on the premise, set forth by the Stoic philosopher Epictetus, that people are disturbed not by what happens to them but by their view of what happens to them, and also on his personal observation that, as he said the other day, “all humans are out of their fucking minds—every single one of them.”

About two hundred humans turned up at the Albert Ellis Institute, whose headquarters are in a six-story town house on East Sixty-fifth Street, to celebrate the founder’s birth with a day of workshops and symposiums, followed by a catered shindig. Ellis is thin and birdlike, with a prominent nose, and he wears large, black-framed glasses. His voice is high and nasal, and when he gets excited it swoops from a goosey honk to a gullish screech. A gastrointestinal infection almost killed him last year, but now he seemed in fine form. Throughout the day, he held forth on a range of topics, from tolerance (“I don’t damn any person, including Stalin, Hitler, and President Bush”) to self-esteem (“the worst sickness known to man or woman, because it says, ‘I did well, therefore I am good,’ which means that when I do badly—back to shithood for me”) and aging (“None of us can change the fact that we’re going to get older and die—too fucking bad”).

Ellis spoke about the “bad things” that happened to him during his childhood, in the Bronx, and about how they led to his early experiments in rational thinking. During a ten-month hospitalization for nephritis, which he got when he was four and a half, he eased his anxiety and loneliness by telling himself, “If I die, I die—fuck it—it’s not the end of the world.” When he was five, his parents found him naked with their neighbors’ five-year-old daughter, playing a clever game with a funnel and a bottle of milk. “That was my first great heterosexual love—a little beauty, a blond bombshell,” Ellis said. “But then her parents moved away and wouldn’t even tell us where they were moving. So, for a while, I was a very depressed child. But I was still able to use the coping statement ‘There will be other women, and I can always have good times with them.’ ” At nineteen, Ellis tried an experiment to conquer his fear of rejection: he hung around the Bronx Botanical Garden, and, whenever he saw a girl on her own, forced himself to start a conversation. “I got to be one of the best picker-uppers of women in the United States, and finally started making it with them, a lot,” he said.

That evening, shrinks drank white wine, talked shop, and spoke about Ellis’s contributions to the profession. The consensus was that his ideas, and his technique of confronting clients with their irrational thoughts, gave birth to the cognitive-behavioral approach that dominates psychotherapy today. “He recognized that we’re all fallible, which is something I try to communicate to my clients,” a psychologist named Marjy Ehmer said. “Though I don’t think it’s necessary to tell them that they’re ‘fucking’ fallible.”

Up in his office, Ellis, dressed in a burgundy silk shirt, gray pants, and thin black socks, took his ease, pashalike, in a leather recliner, and received well-wishers. His assistant, Debbie Joffe, an energetic blond research fellow from Australia, repeated whatever anyone said into a wireless amplifier that beamed directly to Ellis’s hearing aid. One woman told him that he should learn how to read lips. Someone else mentioned that, in the Off Broadway play “Trumbo,” he is referred to as “the greatest humanitarian since Gandhi.” In both cases, Ellis smiled and said, “Could be.” Nicole Kidman was there, of course, in a low-cut black number and sling-back heels. She had come with her father, Tony, who is an Ellis disciple. “You look wonderful,” Kidman said.

“She says you look wonderful, Al,” Debbie said slowly, in a loud voice.

“Thanks—you look O.K., too,” Ellis said.

Later, with a white scarf that had been blessed by the Dalai Lama draped around his neck, Ellis listened to congratulatory messages from Michael Bloomberg, Chuck Schumer, and the Clintons, among others. Someone read an e-mail from President Bush, then handed the printout to Ellis, who glanced at it and let it drop to the floor. There were toasts, too. Janet Wolfe, who lived with Ellis in an open relationship for thirty-seven years (she moved out last year), called him a “closet mensch.”

Since nearly dying last year, Ellis has written two books, and he has been collecting “thousands of articles about how stupid people are” as research for a third, tentatively titled “A History of the Dark Ages: The Twenty-first Century.” He continues to refuse to make himself miserable about anything—yes, anything. He would like to have a romantic partner, and would prefer that other therapists not pass off his ideas as their own, but, he said, “I don’t get angry or upset or depressed about it. That’s the human condition—too damn bad.” Ellis bears no grudge toward the man who beat him out for the top spot on the A.P.A.’s influential-psychotherapist list (that would be Carl Rogers), but he had no kind words for the “bigot” who came in third. “Freud was out of his fucking mind,” Ellis said. “He was as nutty as could be.”