The prevalence of overweight and obesity in Mexican American children 6 to 17 years of age was estimated in 1972 (n = 1269) and 1983 (n = 868). Children were classified as overweight or obese on the basis of the body mass index (weight/stature2), the triceps skinfold, or both, relative to reference data for white children in NHANES-1. Overweight was defined as greater than or equal to 90th percentiles, while obesity was defined as greater than or equal to 95th percentiles of age- and sex-specific reference data. Over the entire age range, there was a significant increase in the prevalence of overweight and obesity between 1972 and 1983, but there was variation with age and sex. Fewer children were classified as overweight or obese when the two criteria were used together than when they were used individually. The results suggest that the body mass index and the triceps skinfold may vary in sensitivity as indicators of overweight and obesity particularly in 10- to 17-year-old children. Children classified as obese by the body mass index had significantly larger estimated midarm muscle circumferences than those classified as obese by the triceps skinfold or by both the body mass index and the triceps skinfold.