We examined the prevalence and socio-behavioral correlates of obesity and overweight among 46,707 immigrant and US-born children and adolescents aged 10-17 years. The 2003 National Survey of Children's Health was used to estimate obesity and overweight prevalence among children in 12 immigrant groups, stratified by race/ethnicity and generational status. Logistic regression was used to examine immigrant differentials in the prevalence and odds of obesity and overweight. Obesity and overweight prevalence varied from a low of 6 and 18% for second-generation Asian immigrants to a high of 24 and 42% for native-born black children (US-born black children with US-born parents), respectively. After adjusting for age, gender, ethnicity, socioeconomic status, perceived neighborhood safety, television viewing, computer use, and physical activity, first-generation immigrant children, overall, had 26% lower odds of obesity than native-born children. Obesity and overweight prevalence was lower for immigrant black and white children than their native-born counterparts, while obesity and overweight prevalence among Hispanic children did not vary significantly by generational status. Compared with native-born white children, the adjusted odds of obesity were 64% higher for native-born blacks, 55% higher for second-generation Hispanic immigrants, and 63% lower for first-generation Asian immigrants. Adjusted immigrant differentials in overweight risks were also marked. Socioeconomic, demographic, and behavioral factors accounted for 61 and 35% of ethnic-immigrant disparities in obesity and overweight prevalence, respectively. Immigrant patterns in childhood obesity and overweight vary substantially by ethnicity and generational status. To reduce disparities, obesity prevention programs must target at-risk children of both immigrant and US-born parents.