Background: Obesity is associated with multiple health problems, often originating in childhood. Objective: The objective was to investigate differences in the development of adiposity from childhood to adulthood as related to race, sex, and socioeconomic status (SES). Design: Individual growth curve modeling for waist circumference, body mass index, and sum of skinfold thicknesses (triceps, subscapular, and suprailiac) was performed in an 11-y cohort study of 622 African Americans and European Americans aged 4.2-27.5 y. We examined the development of adiposity in 2 ways: 1) differences related to race, sex, and parents' education (SES), and 2) differences between obese, overweight, and normal-weight persons at the end of their childhood (> 17 y of age). Results: The sum of skinfold thicknesses was greater in females than in males, with a larger increase with age. Race, sex, and SES showed a complex relation with body mass index and the sum of skinfold thicknesses. The low-SES group showed the fastest increase in waist circumference with age. The obese group showed the most rapid increase in the 3 measures of adiposity. Growth curves for the obese group were distinguishable from those for the normal-weight persons at an earlier age for African Americans than for European Americans. Conclusions: The development rate of adiposity from childhood into early adulthood is influenced by sex and SES but not by race. However, race, sex, and SES had joint effects on adiposity levels. The development of obesity can begin to be distinguished in midchildhood, but the age at which this distinction becomes apparent depends on race. © 2004 American Society for Clinical Nutrition.