A prospective study has been carried out to determine the causes of death and risk factors for survival in 4994 patients referred with a diagnosis of hypertension to hospital specialist clinics and 457 patients treated by their general practitioners for this condition. At the time of entering the prospective study, 69% of the patients were already being treated for hypertension. Four hundred and eleven patients have died, and their causes of death and death rates have been compared with the rates for the population of England and Wales. Ischaemic heart disease accounted for over one-third of the deaths and stroke for one-fifth. The death rates for these conditions were two to five times those expected for men and women aged 50-59 years and up to twice the rate expected for the age group 60-69 years. Survival in these selected patients was impaired by the following independent risk indicators: cigarette smoking, previous history of myocardial infarction or stroke, diagnosis of angina, impaired renal function and raised blood sugar. The following factors were not independent positive risk factors: smoking a pipe or cigars, obesity, a low plasma potassium and an elevated serum uric acid.