From July 1988 to June 1990, we performed an epidemiological study on the prevalence of hypertension and diabetes mellitus (DM) in the Ann-Lo district, a suburban area of Northern Taiwan. One third of the population in the district was randomly sampled. A total of 9087 persons were screened with 67.4% participating. Following completion of the questionnaire blood pressure, 2 h postprandial blood sugar were determined. DM was defined when the blood sugar was over 200 mg/dl or the subject had a diabetic history. Hypertension was defined if the systolic blood pressure was over 160 mmHg or the diastolic blood pressure over 95 mmHg. Statistical comparisons were performed with a chi-square test, analysis of covariance, step-wise multiple regression and Pearson correlation matrix. In this study, the prevalence rate of DM was 2.6% and of hypertension was 6.4%. For those patients 40 years or older, the prevalence rate for DM was 8.0% and for hypertension was 19.7%. The prevalence of hypertension was 24. 8% in overt diabetes and 5.2% in the normal subjects. Analysis of the data between risk factors of DM revealed that DM correlated with age, body mass index, hypertension, smoking, family history of DM and correlated negatively with education. Hypertension correlated with gender, alcohol intake and smoking, sugar level, age and body mass index. The prevalence rate of diabetes and hypertension were quite high in the district and this study pointed out the important risk factors for hypertension and DM in Taiwan.