In order to establish morbidity and mortality in treated patients with essential hypertension, a prospective study was started in 1974. 714 patients were followed for 15 years. Admission criteria included diastolic blood pressure over 95 mmHg during one month on placebo, absence of malignant or accelerated hypertension and no recent (6 month) cardiovascular complication. According to target organ damage, 51% of patients were in WHO stage I, 35% in stage II and 14% in stage III. There were 342 males and 372 females, with mean age 58.7 +/- 9.8 years. Mean initial blood pressure was 181/110 +/- 12/8.9 mmHg. Treatment schedules included diuretics alone (23%), beta blockers alone (32%), diuretic and betablocker (38%), combined therapy with vasodilators (9%) and other forms of therapy (5%). 75 subjects failed to comply with therapy but were maintained in the analysis (intention to treat). A significant reduction in blood pressure was observed in the group as a whole (154/93 +/- 7/9 mmHg). Sustained normalization of BP (< 90 mmHg) was obtained in 40.2% of patients, reductions to between 91 and 100 mmHg in 37.2% and reductions to over 101 mmHg in 22.5% 47 patients died from cerebro vascular complications (15-year cumulative death rate of 12.3%). Total morbidity rate was 40.1% (232 events) with 61 coronary events (13.3%), 43 cerebrovascular events (8.7%), 30 cases of heart failure (12.9%) and 21 cases of renal failure (4.3%). These figures are in agreement with internationally reported ones with the exception of coronary morbidity which appears lower in this study.