Obesity, a major risk factor for a variety of diseases, is more common in Blacks than in Whites. In the current study, a cohort of young Blacks and Whites was followed longitudinally to determine rates of change in body mass index (BMI) and subscapular and triceps skinfold thickness from the ages of 5 to 25 years. A significant difference in the rate of change of BMI (P<.0001) between Blacks and Whites was observed with Blacks gaining at a faster rate. The rate of increase of subscapular (P<.0001) and triceps fat (P<.0001) was significantly higher in the girls than in the boys. We also examined for differences by household income and maternal education level. Children from poorer families had more fat (P<.01 for all three outcomes), whereas education level was not related to the amount of body fat. Differences in the prevalence of obesity between Blacks and Whites and between males and females that manifest during adulthood appear to begin in childhood. The results re-emphasize the important need for early intervention in weight control measures.