BACKGROUND Childhood obesity is related to adult levels of lipids, lipoproteins, blood pressure, and insulin and to morbidity from coronary heart disease (CHD). However, the importance of the age at which obesity develops in these associations remains uncertain. OBJECTIVE We assessed the longitudinal relationship of childhood body mass index (BMI, kg/m(2)) to adult levels of lipids, insulin, and blood pressure among 2617 participants. All participants were initially examined at ages 2 to 17 years and were reexamined at ages 18 to 37 years; the mean follow-up was 17 years. RESULTS Of the overweight children (BMI >/=95th percentile), 77% remained obese (>/=30 kg/m(2)) as adults. Childhood overweight was related to adverse risk factor levels among adults, but associations were weak (r ~ 0.1-0.3) and were attributable to the strong persistence of weight status between childhood and adulthood. Although obese adults had adverse levels of lipids, insulin, and blood pressure, levels of these risk factors did not vary with childhood weight status or with the age (</=8 years, 12-17 years, or >/=18 years) of obesity onset. CONCLUSIONS Additional data are needed to assess the independent relationship of childhood weight status to CHD morbidity. Because normal-weight children who become obese adults have adverse risk factor levels and probably will be at increased risk for adult morbidity, our results emphasize the need for both primary and secondary prevention.