Lisa Whiteaker can’t remember any of her customers by name, but she remembers every monkey she’s ever worked with. When she talks about her cross-country house calls over the last few months, she rattles off monkey species and states like it’s a mnemonic device. “I did a macaque in Arizona,” she says. “I did a capuchin in Florida, a spider monkey in Ohio, and then three capuchins in Chicago.”

Whiteaker, 48, has been a monkey trainer since 1992, and her specialty is privately owned pets. She rehabilitates monkeys adopted by people with no primate experience—customers who, in her words, “saw The Hangover Part II and thought, ‘I want a monkey too!’” By her own estimate, she’s “fixed” 6,700 monkeys so far in her 20-year career, not just in the U.S.: She’s traveled from South Africa to Mexico to Panama to the United Kingdom, and she Skypes with hundreds of troubled monkeys and their owners every week. But getting an appointment to see her isn’t easy. “I’m completely booked until March or April of 2013,” she says.

Business has been good because monkey ownership is at an all-time high. There are no official statistics, but various estimates put the number of domestic monkeys at from 3,000 to 15,000 nationally. Whiteaker, however, suspects it’s more like 45,000. “And that’s not even including research monkeys,” she says. “That’s just in people’s homes.”

Monkeys aren’t a cheap investment. The price tag ranges from $5,000 to $8,000, depending on the size and rarity of the species. At least six states have banned pet monkeys entirely, including California, where Whiteaker has over 200 clients. When they get caught, Whiteaker is usually the first one they call. “What am I supposed to do?” she says. “I can’t get your monkey out of jail! I’m a monkey trainer, not a monkey lawyer.”

Whiteaker, who says she’s widely known by the nickname, “the Monkey Whisperer,” lives in Las Vegas and has a long history of working with animals. She’s a former veterinary technician who once worked for Siegfried & Roy as a dancer and trainer. (She got rid of her white tigers in 2003 after giving birth to her son; “I didn’t want him to be meat,” she says.) She’s the founder of the Southern Nevada Organization of White-Throated Capuchin Monkeys (SNOWCAP), and runs two websites—MonkeyZone and MonkeyPro—at which visitors can learn about everything from monkey nutrition to the proper technique for putting a diaper on a monkey.

She also has personal experience as a monkey parent. She owns five capuchin monkeys—a species most people recognize as the “organ grinder” monkey—all girls, named Cheena, Chelsea, Madilyn, Mugwhy and Tinkerbell. At 18 years, Mugwhy is the oldest and she accompanies Whiteaker on most of her training sessions. “There’s a very good reason for that,” Whiteaker says. “Monkey see, monkey do. I want other monkeys to see that it’s okay to be touched, it’s okay to be loved, that humans aren’t there to hurt them. Mugwhy helps them feel comfortable.”

Before Whiteaker will agree to meet with a new client, she has a strict list of rules. First and foremost, it’s got to be a small monkey. “I don’t do anything bigger than 45 pounds,” she says. This has been her policy since 1994, when she was “beaten up” by an orangutan. “I was babysitting,” she recalls. “I took a little blue bottle away from him, and the next thing I knew, he was on top of me. I’ve never done orangutans again.” She won’t even train chimpanzees, preferring primates that are less likely to overpower her, like marmosets, bushbabies, squirrel monkeys, or tamarins.

All monkeys meeting with her must first be tested for infectious viruses such as tuberculosis, hepatitis, and herpes B. Getting bitten is a regular occurrence in her line of work. “It happens so often, it doesn’t even faze me anymore,” she says. “First they drop you by biting the tendon in the back of your ankle. And once you’re down, then go right for the neck. They’re smart. And mean.” So she won’t go near a new monkey until she’s seen its test results. Whenever possible, she prefers to work with the monkeys alone, without their human counterparts. “I don’t like people,” she says bluntly. “I am all for the monkeys. Everything I do is for the monkeys. But I am not a people person.”

More often than not, Whiteaker says, a monkey’s behavioral problems are solely the fault of the owner. Sometimes it’s poor diet. “They feed them pizza, cookies, hot dogs, all of the things they’re not supposed to have” she says. Sometimes it’s a lack of mental stimulation and distractions. And sometimes the owners are just, well, creepy. Whiteaker recalls visiting a monkey owner in DeKalb, Ill., who seemed confused about the differences between a monkey and a human baby. “I saw a Graco playpen,” she says. “I saw a crib, I saw a car seat, I saw a high chair, I saw all this baby shit. Finally I asked her, ‘Where’s the cage?’ She had no idea what I was talking about.”

Whiteaker doesn’t go easy on her clients. Some people, she says, just shouldn’t have a monkey at all. “Go get a puppy, go get a hamster,” she says. “Something that won’t hurt you.” Monkey maulings are commonplace, most famously in 2009, when a pet chimpanzee named Travis brutally disfigured the face of a Connecticut woman. Every week, Whiteaker meets new monkey parents who she’s certain are flirting with disaster. Most recently, it was a 68 year-old woman in Alabama whose house looked like a monkey crime scene waiting to happen. “She had a capuchin in one cage, a spider monkey in another, and a chimpanzee in another.” Whiteaker immediately called Animal Control, which took all the monkeys away. “I felt bad for doing that,” she says. “But only for like two seconds.”

Even monkey owners who aren’t dangerously outnumbered get the third degree. Whiteaker isn’t afraid to walk out on a hopeless cause, or yell at monkey parents who are terrified of their simian dependents. “I will tell you that you are a wimp,” Whiteaker insists. “You have to have guts to own a monkey. You have to be able to touch your monkey. You have to not be afraid to touch your monkey. That is the only way you will succeed. If you can’t take the initiative, then I’m wasting my time.”

Whiteaker claims she’s had more success stories than failures. “I can take a monkey that’s biting, scratching, and out of control, and put it back in your arms in three to five days,” she says. “I have people who’ve not been able to touch their monkeys, and by the end of the week, after only two sessions, they’re touching their monkey again.”

(This story originally appeared, in a slightly different form, on the Bloomberg Businessweek website.)