Although the benefits of antihypertensive treatment in "young" elderly (under 70 years) hypertensive patients are well established, the value of treatment in older patients (70-84 years) is less clear. The Swedish Trial in Old Patients with Hypertension (STOP-Hypertension) was a prospective, randomised, double-blind, intervention study set up to compare the effects of active antihypertensive therapy (three beta-blockers and one diuretic) and placebo on the frequency of fatal and non-fatal stroke and myocardial infarction and other cardiovascular death in hypertensive Swedish men and women aged 70-84 years. We recruited 1627 patients at 116 health centres throughout Sweden, who were willing to participate, and who met the entry criteria of three separate recordings during a 1-month placebo run-in period of systolic blood pressure between 180 and 230 mm Hg with a diastolic pressure of at least 90 mm Hg, or a diastolic pressure between 105 and 120 mm Hg irrespective of the systolic pressure. The total duration of the study was 65 months and the average time in the study was 25 months. 812 patients were randomly allocated active treatment and 815 placebo. The mean difference in supine blood pressure between the active treatment and placebo groups at the last follow-up before an endpoint, death, or study termination was 19.5/8.1 mm Hg. Compared with placebo, active treatment significantly reduced the number of primary endpoints (94 vs 58; p = 0.0031) and stroke morbidity and mortality (53 vs 29; p = 0.0081). Although we did not set out to study an effect on total mortality, we also noted a significantly reduced number of deaths in the active treatment group (63 vs 36; p = 0.0079). The benefits of treatment were discernible up to age 84 years. We conclude that antihypertensive treatment in hypertensive men and women aged 70-84 confers highly significant and clinically relevant reductions in cardiovascular morbidity and mortality as well as in total mortality.