This retrospective study was based on data obtained from 23 patients over 65 years old (72 +/- 1.04 years) with hypertrophic obstructive cardiomyopathy followed up for 3 years (37.2 +/- 5.4 months) in whom the diagnosis was established essentially on phonomechanographic and echocardiographic criteria under basal conditions or during pharmacodynamic stress testing when the initial examination was inconclusive. Under these conditions, diagnostic catheterisation was only required in 9 cases. The incidence of this disease seems to be substantially underestimated in this age group; clinical symptoms and ECG or chest X-ray changes are often attributed to other pathologies if these patients are not thoroughly investigated. In our experience, patients over 65 years represent 20 per cent of the total population of hypertrophic obstructive cardiomyopathy admitted to our Department during the 6 years' study period. Accurate diagnosis is important because of the therapeutic implications; digitalis and vasodilator therapy especially with nitrate derivatives are poorly tolerated by these patients. Betablockers and verapamil seem to be beneficial, judged on the decrease in the number of symptomatic patients when given these drugs. Only one of the 3 deaths observed in the 20 patients followed-up was attributed to cardiac causes, which seems to confirm the lower mortality rate in older patients with this condition.