1. Males, born between 1900 and 1925, with mild hypertension have been treated for periods varying from 300 to 2000 days.
2. The life and death status of all patients (except two) was known on 1st November 1978.
3. A group of patients with mild hypertension receiving treatment based on a thiazide diuretic had a greater mortality than the other drug-treated group.
4. The increased mortality was caused by an increased number of myocardial infarcts.
5. Elderly male patients with mild hypertension probably have preexisting vascular disease and therapy should not automatically be started. If therapy is started, β-adrenoreceptor-blocking drugs may be a preferred therapy.