The role of coronary artery disease (CAD) in hypertrophic cardiomyopathy (HC) has not been thoroughly clarified. To assess the clinical and prognostic significance of these 2 coexistent diseases, 96 patients with HC (62 men, mean age 45 years) who underwent coronary arteriography and 2-dimensional echocardiography were studied. Significant stenosis (>70%) of 1 or more coronary arteries was detected in 11 patients, all aged >45 years. This group, compared with the other group without significant CAD (n = 85), was characterized by an older age (59 +/- 7 vs 42 +/- 15 years; p <0.05), a greater prevalence of previous myocardial infarction (24 vs 0%; p <0.001), complex ventricular arrhythmias (100 vs 50%; p <0.05), non-obstructive forms (92 vs 46%; p <0.05), dilated (45 vs 7%; p <0.02) and hypocontractile left ventricle (36 vs 6%; p <0.01) and higher mortality (36 vs 8%; p <0.05) during a mean follow-up of 3.6 years. It is concluded that CAD associated with HC is a complex clinic-al syndrome, difficult to diagnose clinically, that can reliably be. recognized by coronary angiography. CAD seems to play an important role in modifying the pathophysiology, the natural history and the prognosis of HC.