The effect of long-term medical treatment in patients with hypertrophic obstructive cardiomyopathy (HOCM) is still controversial, and it is not clear whether propranolol or verapamil should be recommended in these patients. We therefore observed 49 patients (mean age 34.8 years) with hypertrophic cardiomyopathy and mostly mild obstruction for a mean follow-up period of 7.4 years. 13 patients died (10 suddenly and 3 in congestive heart failure) during the observation period (annual mortality rate 3.6%). According to medical treatment the patients were divided into 3 groups: group I consisted of 20 patients who received no medical treatment, group II of 15 patients receiving an average daily dose of 175 mg propranolol, and group III of 14 patients receiving an average daily dose of 360 mg verapamil. The mean follow-up was 6.4 years for group I, 7.0 years for group II, and 3.7 years for group III. 8 patients in group I died during the observation period (annual mortality rate 6.3%), 4 patients died in group II (annual mortality rate 3.8%), and 1 patient died in group III (annual mortality rate 1.8%). Functional limitation was similar in all 3 groups at the beginning and at the end of the study, and mean NYHA class was 1.9 in all 49 patients at the beginning and 1.8 at the end of the follow-up period. Left ventricular peak systolic and enddiastolic pressure were similar during heart catheterization (n = 41) in all 3 groups. Systolic outflow tract gradient at rest was 44 mmHg in group I, 32 mmHg in group II, and 11 mmHg in group III (difference not significant). The actuarial survival curves showed a significant difference (p less than 0.025) between group I and groups II or III.(ABSTRACT TRUNCATED AT 250 WORDS)