CONTEXT: The prevalence of overweight among children in the United States increased between 1976-1980 and 1988-1994, but estimates for the current decade are unknown. OBJECTIVE: To determine the prevalence of overweight in US children using the most recent national data with measured weights and heights and to examine trends in overweight prevalence. DESIGN, SETTING, AND PARTICIPANTS: Survey of 4722 children from birth through 19 years of age with weight and height measurements obtained in 1999-2000 as part of the National Health and Nutrition Examination Survey (NHANES), a cross-sectional, stratified, multistage probability sample of the US population. MAIN OUTCOME MEASURE: Prevalence of overweight among US children by sex, age group, and race/ethnicity. Overweight among those aged 2 through 19 years was defined as at or above the 95th percentile of the sex-specific body mass index (BMI) for age growth charts. RESULTS: The prevalence of overweight was 15.5% among 12- through 19-year-olds, 15.3% among 6- through 11-year-olds, and 10.4% among 2- through 5-year-olds, compared with 10.5%, 11.3%, and 7.2%, respectively, in 1988-1994 (NHANES III). The prevalence of overweight among non-Hispanic black and Mexican-American adolescents increased more than 10 percentage points between 1988-1994 and 1999-2000. CONCLUSION: The prevalence of overweight among children in the United States is continuing to increase, especially among Mexican-American and non-Hispanic black adolescents.