Hypertrophic cardiomyopathy has been investigated mainly at referral institutions. Thus, the clinical history of the disease that emerges from published studies could be influenced by a bias in patient selection. In the present study, we compared the clinical features of an outpatient population of 25 patients who had hypertrophic cardiomyopathy with those reported in 78 studies published during the past five years. In the 25 study patients, age, sex, and the extent of left ventricular hypertrophy, as well as the prevalence of diastolic filling abnormalities, subaortic obstruction, and ventricular arrhythmias, were similar to those in patients described in the literature. Cardiac symptoms, however, were much less severe in the study patients. Eighteen patients (72 percent) were asymptomatic, six (24 percent) had mild symptoms, and only one (4 percent) had moderate-to-severe symptoms. Of 24 patients followed for a mean period of 4.4 years (range, 2.9 to 5.7), none died or had clinical deterioration. Of 3404 patients described in the 78 studies we reviewed, 2483 (73 percent) came from only two referral institutions. Of the 1721 patients in whom severity of symptoms was reported, 757 (44 percent) had moderate-to-severe symptoms. However, 727 (96 percent) of these patients were studied at one of the same two referral institutions. We conclude that the natural history of hypertrophic cardiomyopathy may be more benign than can be inferred from published reports.