Between 1985 and 1987, in two urban and five rural areas in Taiwan, a total of 16,636 subjects aged 40 or over were screened for diabetes mellitus according to the WHO criteria. Four hundred and fifty-two previously diagnosed patients and 274 newly diagnosed patients were found. All were non-insulin-dependent diabetics. The blood glucose control status was compared between the urban and rural previously diagnosed diabetics. Those living in the rural areas were found to have better control with a higher percentage under regular treatment. Stepwise multiple regression failed to discover a significant correlation between control status and any of the following factors: sex, age, body mass index (BMI), diabetic duration, treatment regularity, exercise, occupation, education, family income and the presence of hypertension or large vessel diseases. About 30% of the patients in rural areas and 40% in urban areas were poorly controlled. This indicates that our diabetic control program should be strengthened.