The prevalence of hypertension, effectiveness of blood pressure control and compliance, and the effectiveness of treatment on 18-month overall mortality and development of cardiovascular disease in an elderly Chinese population were studied. The study group examined were aged 70 years and over, and consisted of a random sample of subjects on the Old Age and Disability Allowance register. They were stratified by sex and 5-year age groups from 70-74 to 90+ years. Information obtained at baseline included medical history, use of drugs, and measurement of blood pressure. Subjects with a blood pressure > 160/90 were classified as hypertensive. The overall prevalence of hypertension was 48%, 19% being undiagnosed. Among subjects with a known history of hypertension and taking drugs, only approximately half had adequate control (BP < or = 160/90). One fifth of those with a known diagnosis of hypertension were not taking drugs. Subjects who developed stroke had a higher mean systolic and pulse pressure at baseline; no difference in mean pressures was observed for overall mortality or development of heart disease. No difference in mortality or development of cardiovascular disease was observed between the following groups: known history of hypertension and taking medication with controlled blood pressure, known history and taking medication and blood pressure poorly controlled or not taking drugs, and normal blood pressure with no history of hypertension.