The growth status and densitometric estimates of body composition are considered in a cross-sectional sample of 95 Mexican-American boys, 9 through 14 years of age, from lower socioeconomic circumstances. A series of 19 measurements were taken on each boy, including measures of size, proportions, skeletal breadths, limb circumferences, skinfolds, and grip strength. Body density was determined by underwater weighing and residual volume was predicted. Density determinations were converted to percentage body fat using the average of two estimates from the equations of Brozek et al. (1963) and Siri (1956). Relative fatness was also converted to lean body mass and fat weight in kilograms. The growth status of the boys was compared to reference data for American White boys in the U. S. Health Examination Survey. The Mexican-American boys are shorter and lighter than the reference data, and smaller in all anthropometric dimensions except skinfolds, which are variable. The subscapular and midaxillary skinfolds are similar in the two samples, while the triceps, medial calf, and suprailiac skinfolds are thinner in Mexican-American boys. Regressions of the four body composition estimates on age show significant age effects only for lean body mass and fat weight. Density and percentage fat do not vary significantly with age. Compared to samples of boys in the same age range, the Mexican-American boys generally have a greater body density. Correlations between skinfold thicknesses and body density are generally lower in the Mexican-American boys compared to other samples. Two equations for the prediction of body density in Mexican-American boys are offered.