IT'S HARD ENOUGH to run your own business. How about two or three?

For Linda Fong of San Leandro, Calif., it's more like four. Just this month, Fong opened up a Fastsigns franchise in nearby Hayward (she already owns a Fastsigns sign-company shop in Oakland). And that's on top of the Plato's Closet teenage-clothing store she opened in 2005 and the hair salon that she founded — and still operates with her husband — 23 years ago.

"This isn't for everyone, but I thrive on change," she says. "Maybe I'm an adrenaline junkie."

Indeed, business owners who run multiple companies say it's something like an addiction — they get a thrill starting a brand-new business, even if they have to commit a huge sum of time and energy getting the venture off the ground. They also reap financial rewards: A 2007 report from the Small Business Administration shows that multiple-business owners are the most prosperous of entrepreneurs, with nearly three-fourths classified as high income and one-half as high wealth. People who own more than one business make up about 18% of all small-business-owning households.

But it's definitely not for everyone, especially an entrepreneur who has trouble delegating responsibilities or relying on others to manage day-to-day operations. Mike McNulty, who started advertising agency Prime Source in Williamsville, N.Y., about 20 years ago, opened up companion shop Prime Promotions, an Adventures in Advertising franchise, in 2000. Successfully managing both is about having "the right people in place — and you have to believe in those people," says McNulty, who has a total of 14 employees and relies on wife Tina to run Prime Promotions.

In fact, letting go of "control freak" tendencies is perhaps the single most important thing a multiple business owner can do to manage operations effectively, while still enjoying a personal life, says Corinne Post, assistant professor of management at Pace University in Pleasantville, N.Y. "It's a business imperative rather than a character correction," she says. Assigning everyday tasks to employees gives entrepreneurs more time to be reflective and innovative, and "minimizes or reduces the amount of time [they're] spending putting out fires," she says.

That's what Rick Maffezzoli of Timonium, Md., has done over the years in order to operate several entrepreneurial ventures, yet still enjoy "some flexibility to adjust my own schedule, so if I need to spend time with my kids, or have a doctor's appointment, I can control it."

Maffezzoli has installed trusted managers at two businesses he currently owns, Gold's Gym and a Tan Co. tanning salon, and plans to do the same when he opens up five more salons in coming years. He relies on his BlackBerry to keep abreast of what's going on at both locations. And most importantly, he's learned to adopt the relaxed attitude of "nothing is going to burn down" in his absence. "And if it does, what are you going to do about it," he says, in laidback fashion.

Keith Carroll, on the other hand, is still trying to figure how to take time off or "sneak away" since starting Premier Garage, a custom-garage furnishings shop, in 2005 literally across the street from garage-door company Superior Door Co., which he founded in 1993. "It gets so hectic sometimes," says Carroll, of Twin Falls, Idaho. He hasn't taken a vacation, but he's learned to quit working on Saturdays and to schedule personal activities during the week on his calendar. "If you're not organized, I don't know how you'd pull it off," he says.

Carroll also says it helps to attend networking events through the local Chamber of Commerce or builders' association. "It gets you out of the shop environment and rubbing shoulders with other business owners who are having the same problems," he says. But will he open another business? "No," he says. "Let me make that real clear. No."

A number of small-business owners who start other ventures choose the franchise model because of its tried-and-tested approach (see our story), which can ease the process of starting up. Other multiple-business owners say they keep it simple by choosing locations that are close together and reducing duplicative jobs. McNulty, for instance, runs his Prime Source and Prime Promotions companies out of the same leased space, with a shared receptionist and accountant.

While work-life balance can be a challenge for any business owner, those who run multiple businesses may find it particularly tough to make time for personal lives. But those same skills at delegating in the work place can come in handy at home, says Neen James, a productivity expert in Doylestown, Pa. She recommends that multiple-business owners outsource as much as possible, whether that's grocery shopping, housekeeping, lawn mowing, even holiday gift buying. "Stop spending so much time doing errands," she says. Another option is to hire a virtual assistant, who can handle any number of administrative and personal tasks, she says. One place to look is the International Virtual Assistants Association.

Fong, who just opened her fourth business, says the best way to put things in perspective is, quite simply, to start more businesses. "Personally, I just found owning one business is more time-consuming than owning several," she says. "When you own one, you eat, live and breathe it." Owning multiple businesses is a lot like having many children — "you kind of relax a little bit more" with each one, she says.

("Work & Life," a weekly column written by Colleen DeBaise for smSmallBiz.com, advises entrepreneurs on how to better balance their lives. Write to her at cdebaise@smartmoney.com.)