Mexican Americans have a higher prevalence of NIDDM, more overall obesity and more centralized adiposity than non-Hispanic whites, but have thus far not been characterized as to whether they have greater upper body adiposity. Waist-to-hip circumferences (WHR, a measure of upper body adiposity) and subscapular-to-triceps skinfold ratios (centrality index, a measure of centralized adiposity) were determined in 725 Mexican Americans and 226 non-Hispanic whites as part of the San Antonio Heart Study, a population-based study of diabetes and cardiovascular risk factors. Mexican American females had higher centrality indices and WHRs than non-Hispanic white females, even after adjustment for demographic (age, menopausal status) and behavioral variables (body mass index, parity, cigarette smoking, alcohol consumption, exercise, and oral contraceptive and estrogen use). Mexican American males had higher centrality indices than non-Hispanic white males, but differences in WHR disappeared after adjustment for overall adiposity (body mass index). Of the demographic and behavioral variables, only age and body mass index were consistently related to regional body fat distribution. The lack of an association between body fat distribution and behavioral variables suggests that genetic factors may play the principal role in determining body fat distribution. Surprisingly, the distributions of centrality index and WHR were relatively independent of one another suggesting that they may be used as distinct, independent predictors of metabolic diseases.