Patients in this study were assessed by coronary angiography because of classic effort angina and a positive exercise test. Of these patients, 320 had untreated primary hypertension and 320, similar in age and gender distribution, were normotensive. In all patients coronary angiography documented that at least one major epicardial branch was restricted by 50% or more. Prevalence of single- and double-vessel disease in the fourth and fifth decades of life was similar in the two populations and in both tended to decline with age. Prevalence of triple-vessel disease was also similar in the two populations in the fourth and fifth decades; in either population it rose with age and reached a peak at the seventh decade of life. The percentages of hypertensive patients in the sixth and seventh decades with triple-vessel disease was significantly (p less than 0.01) greater (40% and 50%, respectively) than the corresponding values in normotensive individuals (25% and 31%, respectively). The left main coronary artery was not significantly more involved in the high blood pressure group. Pressure was moderately and similarly raised at any age in hypertension; serum cholesterol and triglyceride levels, blood glucose, and smoking habits were comparable in the two populations. These results suggest that hypertension does not accelerate the appearance of significant coronary narrowing or multiple vessel involvement. Starting from the sixth decade, the natural age-related evolution of coronary disease seems to be aggravated in hypertensive subjects, as reflected by an augmented number of diseased vessels. This process is probably related to high blood pressure in itself; whether the severity of hypertension might also exert an influence is not deducible from this study.(ABSTRACT TRUNCATED AT 250 WORDS)