Epidemiologic studies of migrant populations provide very promising clues towards understanding the roles of genetics and environmental factors in the etiology of diabetes mellitus. Populations of Japanese ancestry are of particular interest due to marked differences in prevalence rates of non-insulin dependent diabetes (NIDDM) when comparing those living in Japan with those who migrated to western countries. Brazil offers very favorable conditions of the study of diabetes in the Japanese origin population. Presently, Brazil has the largest population of Japanese ancestry outside Japan. A cross-sectional study comparing first (Issei) and second (Nisei) generations of Japanese-Brazilians living in the city of Bauru, in the industrialized state of São Paulo, southeast of Brazil, was carried out between May and November 1993. The study sample consisted of all first generation (127 men and 111 women) and a random sample of second generation (136 men and 156 women) aged 40-79 years. Results show that: 1--The prevalence of diabetes in Japanese Brazilians (12.8 and 16.2% for first and second generations) are higher than the rates reported for Japan at comparable age-groups. 2--Comparing generations, the age-adjusted prevalence of diabetes was higher in the second generation only for men (men: 12.4 vs. 21.7%; women: 11.6 vs. 11.4%). 3--Obesity was more prevalent in the second generation among men (Men: 34.6 vs. 45.7% women, 39.6 vs. 40.8%).