(FORTUNE Magazine) – DONNY DEUTSCH, THE MOST FAMOUS man in the advertising business, strolled into the Regency Hotel in New York City. He stopped at a mirror in the lobby and looked himself over. He seemed pleased with what he saw. Then he headed toward the restaurant to talk about his new book, Often Wrong, Never in Doubt: Unleash the Business Rebel Within.

Tan and fit at 47, Deutsch considers himself a "decent enough looking" guy. He says as much in Often Wrong, Never in Doubt. There's an entire chapter devoted to how Deutsch decided to get into shape in 1997 after friends of a woman he was dating teased her for being with "that fat older guy." Deutsch started working out five days a week. He's shed 45 pounds and writes that he's never been in better condition: "It's nice to know that you can physically take whomever you're doing business with."

Donny Deutsch is certainly not the first famous adman to write a self-promotional book. In 1962, David Ogilvy, the most revered Madison Avenue figure of his generation, penned Confessions of an Advertising Man, in which he quoted Toynbee and Shakespeare while explaining how to manage an ad agency, get clients, and make television commercials. Ogilvy's book sold millions of copies. Often Wrong, Never in Doubt is also a branding effort. But the book, which Deutsch co-wrote with author Peter Knobler, is more about Donny Inc. than Deutsch Inc., his advertising agency. It is a primer on how to become a buff, swinging multimillionaire ... like Donny Deutsch! "I like to think of it as Jack Welch raw," he says over coffee at the Regency.

He spends the bulk of the book talking about how he built Deutsch Inc. into a successful company that he sold to the Interpublic Group in 2000 for "close to $300 million." (The true value of the deal was closer to $275 million.) He gushes about his talk show on CNBC, The Big Idea With Donny Deutsch: "I have my own prime-time TV show. That's insane!" And true to his bad-boy form, in a chapter called "Women Are Muses" he writes: "I don't think there's been a day in my business career when there hasn't been some woman at work that I fantasized about."

You might want to think twice before taking career advice from Deutsch, though. At a time when brand Donny has never been bigger, the ad agency that bears his name is having a dismal year--its worst in quite some time. In September, Credit Suisse First Boston estimated that his agency had lost nine accounts--including Mitsubishi, Bank of America, and Revlon--with total billings of $849 million in 2005. On the new-business side of the ledger, Credit Suisse reported that the agency had won only four accounts, with total billings of $44 million. (The agency disputes these figures but doesn't offer much in the way of specifics.) There have been layoffs. And on Sept. 23, Deutsch Inc. announced that Linda Sawyer, Donny's second in command, was replacing him as CEO. Deutsch remains the agency's chairman and, as he says, its "spiritual leader."

Deutsch insists that his self-branding campaign has nothing to do with the agency's woes. "I don't think you can draw the line between, oh, Donny's stepped way back now and that's why the agency's had rough times." Sawyer, too, says that Donny's self-promotional efforts outside the firm are "irrelevant," adding, "He is not interacting with clients, he's not interacting with most of our employees."

Others in the ad world find these protests laughable--and they make a legitimate point. "There's just this big disconnect between brand Donny and Deutsch Inc.," says Rob Schwartz, executive creative director of TBWA/Chiat/Day in Los Angeles. "Here's this guy who has positioned himself as the voice of the ad business. Clients see him on TV and say, 'I like this guy.' But when they go to his agency, they meet these other people who say, 'No, we're the brains behind everything now.' The client goes, 'Huh?' "

Deutsch Inc. has never been known for doing industry-transforming work like TBWA/Chiat/Day's Apple ads or Wieden + Kennedy's campaigns for Nike. What set Deutsch Inc. apart was Donny. He doesn't write about this in his book, but early in his career, when he was frustrated with his lack of press coverage, he went to New York public relations guru Howard Rubenstein for help. Rubenstein told Deutsch that veteran Madison Avenue provocateur Jerry Della Femina was leaving the stage, and there was an opening for another loud, irreverent adman. Deutsch filled the void (he says he doesn't remember any such conversation, though Rubenstein does).

He set out to brand himself as the "brash, upstart Ad Guy of the Generation," he writes in the book. He told USA Today he was thinking about smashing up a Jetta after making an unsuccessful pitch for Volkswagen's advertising business. He smoked cigars. He wore T-shirts, jeans, and cowboy boots. He swore like a longshoreman. "Donny understood the agency needed to be a brand," says Greg DiNoto, a former Deutsch Inc. creative director. "He understood the way to do that most effectively was through him."

It worked. Everybody wanted to meet Madison Avenue's new wild man. By 2000, Deutsch writes, the agency's annual billings had ballooned to $1.5 billion. Larger advertising and marketing companies wanted to buy his agency, and he cashed out at the top of the market--just before Madison Avenue fell into the worst advertising recession in history.

By then Donny felt he'd "won the game" on Madison Avenue, as he puts it in Often Wrong, Never in Doubt, and he needed "another mountain" to climb. Before long Deutsch's public relations people were calling reporters to say Donny was rebranding himself as a media guy. He invested in an independent movie-production company. He made an unsuccessful run at New York magazine. The thing that worked best for him was his CNBC talk show, which, even though it hasn't attracted a lot of viewers, has made him a celebrity.

Deutsch also ramped up the outrageous self-promotional behavior that served him so well on Madison Avenue. In a New York magazine profile, he joked about sleeping with another woman in the presence of his wife (they are now separated). He interviewed porn star Jenna Jameson on Big Idea and then told Playboy, "I was certainly flirting with her as hard as I could. And let's emphasize the word 'hard.' " In August, Publishers Weekly included in a review of Often Wrong, Never in Doubt a passage from the uncorrected galleys describing, in exuberantly salacious language, the author's attitudes about mixing sex and business. (He was for it, of course. But after HarperCollins complained, Publishers Weekly removed the quotation from its review on Amazon.com, and it doesn't appear in the published book.)

Deutsch's boss, Interpublic CEO Michael Roth, says, "There's no question he's getting more exposure. We want to see that converted to more revenue." Deutsch may have other plans, though. "I really believe I'll be mayor of New York someday," he says."I know I have the financial resources to do it."

Maybe that would be the best thing for Donny Inc. and Deutsch Inc. There'd be no more confusion. They'd finally have to sever their ties.

DEVIN LEONARD, a senior writer at FORTUNE, can be reached at dleonard@fortunemail.com.