The purpose of this study was to compare the prevalence of diabetes and risk factors for the disease in three ethnic groups in Taiwan; the Hakaas, Fukienese, and aborigines. A cross-sectional study of men and women aged 50-79 years were invited to attend a standardized interview and physical examination. Diabetes mellitus was defined as a fasting plasma glucose (concentration of greater than or = 126) or a previous diagnosis of diabetes. Demographic, socioeconomic, and risk factor data were obtained. A total of 1293 persons (468 Hakaas, 440 Fukienese, and 385 aborigines) completed the examination. Hakaas had the highest age-adjusted prevalence of diabetes, 17.9% in men and 15.5% in women, followed by Fukienese, 14.5% in men and 12.8% in women. Aborigines had a prevalence of 10.0% in men and 13.3% in women. Diabetes prevalence was positively associated with family history of diabetes, obesity, hypertension, and hypertriglyceridemia. The ethnic variation in diabetes prevalence was reduced after adjustment for age, sex and significant factors. The multivariate-adjusted odds ratios (95% confidence interval) were 1.27 (0.76-2.12) for Fukienese and 1.44 (0.89-2.33) for Hakaas compared with aborigines. Diabetes mellitus is a major public health problem in Taiwan and warrants prevention efforts tailored to the country's different ethnic groups.