Two hundred one patients with essential hypertension, who had studies of their renin-aldosterone system performed between April 1967 and December 1972, were surveyed for myocardial infarction or cerebrovascular accident. Of the patients, 42% had low plasma renin activity. Myocardial infarctions or cerebrovascular accidents were documented in 15% of those with low plasma renin activity and in 5% of those with normal plasma renin activity. When adjustments were made for differences in age and blood pressure, a protective effect in low-renin hypertension was not evident. When black patients were considered separately, there was no difference in diastolic blood pressure; however, vascular complications were not less frequent in low-renin hypertensives. The results suggest that low plasma renin activity does not protect against the development of vascular complications in essential hypertension.