A picture of Twiggy on the cover of a Vogue magazine prompted Patricia DePol to go on a diet back in 1969. Then a 16-year-old student at Park Ridge (N.J.) High School, DePol intended to lose four to six pounds from her 5-foot-4, 117-pound frame.

"It just snowballed," recalls DePol, now 33. After she lost five pounds she would tell herself, "let me lose another five pounds . . . It feels good. I don't really want to lose the weight, but let's lose another five pounds ."

Six months into the diet DePol weighed 90 pounds.

"I went on a diet that I couldn't stop," she says. "I couldn't make myself eat. The biggest fear is gaining weight and losing control."

Her parents took her to a pediatrician, a psychiatrist, and back to the pediatrician. But DePol continued to exercise obsessively and not eat.

When she was a senior in high school and down to 69 pounds her doctors hospitalized her for 5 1/2 months. Through behavior modification and individual and group therapy, she got her weight up to 105.

But five weeks later, after arriving at Juniata College in Huntington, Pa., she began to lose weight again. Within a week she weighed 95; by the end of the year, 73.

DePol finished college with a degree in psychology and returned to her parents' home to resume therapy while she worked as a waitress.

"I just had to find out what was going on in me," she says, "why my self-esteem is tied to what the scale says."

DePol says she has had to relearn when she is hungry, how to eat and how to socialize.

"You are completely out of touch with all your needs because anorexia has taken over and become your personality." The process has been a gradual one.

"It's not like the sky opens up and you have your answers," she says. "It takes a long time."

Today, DePol weighs 125 and is finishing a graduate degree in family counseling. She owns a jazz club with her fiance in Cliffside Park, N.J.

In upper-middle- to upper-class families, anorexia nervosa affects an estimated one or two of every 150 females between age 12 and 30.

The disorder, first identified in Britain in 1689, became widespread in the mid-70s and has continued to grow in the '80s.

People -- typically young women -- with anorexia nervosa restrict their food intake until they lose at least 25 percent of their usual body weight. Sometimes they binge, too.

In bulimia, a related disorder, patients have periods of uncontrollable binging followed by self-induced vomiting or purging with laxatives. Both anorexics and bulimics are obsessed with being thin and suffer from a distorted body image and family pathology, often associated with issues of a daughter's separation, identity and sexuality.

Taking weight loss to an extreme is a way of gaining control, feeling effective, but not dealing with issues of adulthood.

"Anorexia is not about being thin," says Dr. Victoria Casey, a clinical psychologist and coordinator of research and clinical services at Georgetown University Hospital. "It's really about control, identity, competence. It all gets put on this external thing weight , which is a number."

The road to recovery begins with normal eating habits, emphasizing foods of high-caloric density.

"The underlying issues are going to continue to be there after they gain weight," Casey says, " but they have to weigh more."

Treatment usually includes medical support for weight-gain, and psychotherapy to explore the underlying issues that led to the symptoms.