The prevalence of diabetes in Central America was somewhat greater than in East Pakistan and Malaya, less than in Uruguay and Venezuela, and substantially less than in affluent societies such as the United States. Differences in prevalence among Central American countries were modest but probably significant in some instances. In all Central American countries diabetes was more common in females but this difference was probably attributable to the greater adiposity of the women. Age-matched populations from eleven different countries of three continents have now been tested using standardized methods. Prevalenceof diabetes varied greatly, and differences were more related to environment than to race. These results support the hypothesis that environmental factors can increase or reduce prevalence by several-fold.