The aim of this study in 341 men (aged 68 years) without history of ischemic heart disease was to study the relation between hypertension and silent ischemic-type ST segment depression during ambulatory long-term electrocardiographic recording and to assess the influence between these two variables on cardiovascular morbidity and mortality rates. Seventy-nine men (23%) demonstrated one or more episodes of silent ischemic ST segment depression. One hundred and sixty-seven men (49%) were considered to have hypertension (i.e., they had a diastolic blood pressure of 95 mm Hg or greater or were treated with antihypertensive therapy). Forty-nine (72%) of the 68 treated hypertensive subjects were classified as uncontrolled (i.e., their diastolic blood pressure was 95 mm Hg or greater). The occurrence of ischemic ST depression was higher in hypertensive men (28%) than in normotensive men (19%). The highest incidence of ischemic ST depression (41%) was observed in treated hypertensive men with inadequate blood pressure control. Cardiac event rate during a 53-month follow-up was 6.6% in hypertensive men and 4.6% in normotensive men. Uncontrolled treated hypertensive men had a higher event rate (14%) than hypertensive men overall. Hypertensive men with inadequate blood pressure control and who demonstrated ST segment depression had the highest event rate (25%).