Robert T. Brown’s patients may be obese or anorexic; sexual innocents or infected with chlamydia; male or female; jocks or goths; abusers of alcohol, Ecstasy or over-the-counter drugs; tattooed, pierced, pimpled; surly and stressed; or just mortified by their molting, rebelling bodies.

Diverse and challenging, they share at least one common factor, which brings them to the attention of Dr. Brown and his colleagues. They are all adolescents.

“We do dermatology, sports medicine, psychology, gynecology, orthopedic issues, psychosocial issues, substance abuse and address problems of developing sexuality,” said Dr. Brown, a specialist in adolescent medicine.

“We’re highly trained generalists for a specific population — like gerontologists,” he said. “But either we’ve done a poor job of marketing ourselves or there is something about the field.”

Adolescent medicine might be expected to be booming. The nation has about 40 million people ages 10 to 19, a patient population that experts say is vulnerable to a growing array of behavior-related health problems.

But a decade after adolescent medicine became board certified as a subspecialty, it is in little demand by doctors seeking to advance their careers. Small wonder the public is generally unaware of the field: according to the American Board of Medical Specialties, only 466 certificates in adolescent medicine were issued from 1996 to 2005. In the same period, 2,839 were issued in geriatric medicine.

But the availability of doctors and nurse practitioners dedicated exclusively to adolescent care is still the exception. Their numbers are so limited that many cannot take on adolescents as primary-care patients; the patients see them on a temporary referral basis. Of those teenagers who are insured and who continue to see a primary-care doctor, a vast majority remain with the pediatricians or family doctors who have cared for them since diaperhood.

That job has become more time-consuming and complex. “Adolescents are not big children and they’re also not little adults,” said Dr. Walter D. Rosenfeld, an adolescent medicine specialist.

They are not just a bridge population, he and many others maintain, but their own stop in the road. During adolescence, people need to learn how to take responsibility for their health and, eventually, to become health care consumers, independent of their parents.

At programs that are sensitive to adolescents, this changing dynamic is negotiated deftly but firmly. Recently, at an eating disorder clinic at the Goryeb Children’s Center at Overlook Hospital in Summit, N.J., a nutritionist beckoned to a teenager in the waiting area. The girl’s mother stood to follow. But after the girl slipped into the exam room, the nutritionist closed the door.

“Oh, I thought I was going in with her,” the mother said to no one in particular. “Guess not,” she added with a small laugh of embarrassment.

Organizations like the American Academy of Pediatrics and the Society for Adolescent Medicine recommend that primary-care physicians monitor teenagers for drug and alcohol use, smoking, sexual activity (including disease prevention and use of birth control), physical activity, nutrition, depression, school behavior and social pressures. Yet various studies have shown that many pediatricians feel inadequately prepared to address most of these issues.

A father in Indianapolis, who did not want to identify himself to protect the privacy of his shy 12-year-old daughter, said: “Our pediatrician is a great guy around everyday things, but he’s not adolescent-focused. He won’t ask her about sex or alcohol or drugs. It’s just not in his repertoire. He’s a baby doctor, oriented toward the quickie office visit.”

Because teenagers seek out doctors infrequently, pediatricians have to grab at any opportunity to reach them, said Dr. Susan R. Brill, director of adolescent medicine at the Children’s Hospital at St. Peter’s University Hospital in New Brunswick, N.J.

“I could see a boy with strep throat and he’ll grunt at me and we’ll be done in five minutes,” she said. “Or I could take a little more time to talk to him — I might find out about sexuality issues that way. If a kid is coming in for bronchitis, I’ll get the parent out of the room and ask the kid if he’s smoking. If a kid is on a sports team and comes in with an injury, is the pediatrician talking about weight and eating and steroid abuse?”