This study assessed how socioeconomic status (SES), race/ethnicity, and birth weight interacted to predict differential patterns of body mass index (BMI) growth among U.S. children born in the early 1990s. Three BMI growth trajectories emerged--one above the 50th percentile across the age range of 5 to 14, one in which children rapidly became obese before adolescence, and one where children started out and remained seriously obese. Hispanic and African American children were more likely to show accelerated patterns of weight gain as were those of lower SES and/or higher birth weights. However, SES interacted with both race/ethnicity and birth weight. For girls of all race/ethnicity groups tested, lower SES and higher birth weights predicted membership in the seriously obese BMI growth trajectory. For African American and Asian boys, however, the higher the SES the more likely they were to be on a trajectory for rapidly developing obesity by early adolescence. (Contains 5 figures and 5 tables.)