INTRODUCTION: Although socioeconomic differences in prevalence of obesity are well documented, whether patterns of weight gain during key periods of growth and development differ among youth from different socioeconomic backgrounds is unknown. This study examines socioeconomic disparities in overweight status and 5-year weight gain among adolescents. METHODS: Project EAT (Eating Among Teens)-II followed a socioeconomically and ethnically diverse sample of 2,516 adolescents from 1999 through 2004. Mixed-model regression analyses examined longitudinal trends in overweight status as a function of socioeconomic status (SES). RESULTS: Girls and boys in the low-SES category were more likely to be overweight than were those in the high-SES category. Boys in the high-SES category showed a significant decrease (P = .006) in overweight prevalence between 1999 and 2004, whereas boys in the low- and middle-SES categories showed no significant change. Girls in the low-SES category showed a significant 5-year increase (P = .004) in overweight prevalence compared with a stable prevalence of overweight among girls in the middle- and high-SES categories. CONCLUSION: Our data show continued and, in some cases, increasing socioeconomic disparities in risk for overweight. Youth from low-SES backgrounds are at increased risk for overweight and are more likely to remain overweight (boys) or become overweight (girls). Designing obesity prevention and treatment interventions that reach and address the unique needs of youth and families from less-advantaged socioeconomic backgrounds is a public health priority.