A heart attack ended her dad's life when he was 43. Her mother died of bone cancer at 68. Heart disease and cancer killed several other relatives on both sides of her family, many of them in their 50s.

With such a foreboding history, Janet Kennedy, 47, is not about to leave her health to fate.

"When my dad was 36," she says, "he couldn't even lift my little brother, who was 2, or mow the yard or do any of the things you would expect a man of 36 to be able to do. It made me very conscious of my health."

It also inspired her to compile — and act on — a family health history, a move U.S. Surgeon General Richard H. Carmona would applaud.

Last year he launched the Family History Initiative, saying that "knowing your family's medical history can save your life."

In cooperation with the U.S. Department of Health and Human Services, Carmona introduced a computer-based tool called "My Family Health Portrait." It encourages users to trace illnesses that run in their families and begin tests, treatments and lifestyle modifications before disease is evident.

David Johnson, physiology department chairman at the University of New England's College of Osteopathic Medicine in Biddeford, Maine, calls waiting for symptoms to appear "an ineffective way to practice medicine."

By that time, he says, "the disease is winning."

Family history, the strongest risk factor for many health conditions, is the best way to identify people with underlying problems early enough to intervene, he says.

Johnson is co-author with physician David Sandmire and medical writer Daniel Klein of "Medical Tests That Can Save Your Life" (Rodale, $14.95).

They recommend expanding family history to include your personal medical information (rheumatic fever at age 6, for example, treatment received, residual effects) and social history (diet and exercise habits, cigarette or alcohol use, exposure to sun or environmental toxins, and so on).

Major genetic disorders such as cystic fibrosis and Huntington's disease require extensive medical intervention. But awareness of other illnesses for which race or ethnicity put you at risk may allow you to alter their course noninvasively.

"Health history is particularly important for black people," says Arnold Williams, 60, noting the number of diseases that occur more frequently and more severely in his race than in whites. "It's just a reality you have to face. It means you have to get more checkups."

Family eating patterns during his childhood and a history of high blood pressure among relatives challenge him, he says. His biggest battle has been giving up cigarettes, which contribute to a number of conditions that afflict blacks.

"I quit, then I lapse," says Williams, a retired Tempe, Ariz., Army colonel who teaches photography and writes for state and national publications. "Right now I'm quitting again."

More successfully, he follows a modified South Beach Diet, bicycles and walks, habits that can lower blood pressure and the risk for heart disease, stroke, diabetes and prostate cancer.

"My blood pressure has come down significantly," he says, "and I lost 25 pounds in about two months without starving myself."

Guided by a detailed health history that dates back to her great-grandparents, Kennedy, of Scottsdale, Ariz., never has smoked.

She has had her cholesterol tested at least once a year since she was 23. She had a colonoscopy, typically recommended starting at age 50, early this year. And she watches her weight, exercises and takes baby aspirin to prevent heart problems.

Her vigilance extends to her husband, Rick, and their sons, Michael, 18, and Austin, 16. They get cholesterol checks, too, and when the boys were growing up, cookies never were offered as a reward for good behavior.

All four Kennedys play sports.

A take-control approach like hers, Maine professor Johnson says, "makes it fairly easy to avoid some of the medical horror shows that we run into in our 50s and 60s.

"As a hospice worker, I've seen enough people with a 'fate is fate' attitude. Then they get a fatal disease and they're only 50 and they say, 'If only I had ...' "