WASHINGTON (AP) -- Make Grandma spill the beans:  Uncovering all the diseases that lurk in your family tree can trump costly genetic testing in predicting what illnesses you and your children are likely to face.

It may sound old-fashioned, but a Cleveland Clinic study comparing which method best uncovered an increased risk of cancer helps confirm the value of what's called a family health history.

All it costs is a little time questioning your relatives, yet good family health trees are rare.  A government survey estimated less than a third of families have one - and time-crunched doctors seldom push their patients to remedy that.

"I view family health histories as back to the future," says Dr. Charis Eng, a cancer geneticist at the Cleveland Clinic's Genomic Medicine Institute. "It's the best kept secret in health care."