The association between acculturation to a Western lifestyle and prevalence of diabetes was examined among 8,006 Japanese-American men in Hawaii with varying degrees of exposure to traditional Japanese social and cultural lifestyles in 1965-1968. A reduced prevalence of diabetes was observed among the men who had retained a more Japanese lifestyle. These men also reported higher levels of physical activity and consumed more carbohydrates and less fat and animal protein in their diet. An inverse association between diabetes and being born in Japan was observed independent of age, body mass index, physical activity, and percentages of calories from fat or carbohydrates (odds ratios = 0.67 and 0.66, 95% confidence intervals 0.49-0.93 and 0.48-0.91, respectively). The number of total years lived in Japan was inversely associated with prevalent diabetes after controlling for age, body mass index, and physical activity (odds ratio = 0.81, 95% confidence interval 0.68-0.96). Current Oriental diet (compared with Western diet) was inversely associated with prevalent diabetes after controlling for age, body mass index, and physical activity (odds ratio = 0.71, 95% confidence interval 0.50-0.98). These findings suggest that living a Japanese lifestyle is associated with a reduced prevalence of diabetes.