The morphologic apical form of hypertrophic cardiomyopathy (HC), in which left ventricular (LV) wall thickening is confined to the most distal region at the apex, has been regarded as a phenotypic expression of nonobstructive HC largely unique to Japanese patients. To investigate this question further, we directly compared unselected and regional hospital-based cohorts of adult patients with HC ( > or =18 years of age) from Japan (Kochi; n=100) and from the United States (US) (Minneapolis; n=361). Japanese and American patients with HC had similar clinical features and did not differ significantly with regard to the severity of symptoms and frequency of outflow obstruction. Although Japanese and American patients also showed similar maximum LV thickness, they differed significantly with respect to the distribution of LV hypertrophy. In particular, the segmental form of HC, with hypertrophy confined to the LV apex, was more frequent in Japanese patients (i.e., apical HC, 15% in Japan vs 3% in US, p<0.0001). Giant negative T waves were also more common in Japanese patients with HC (26% vs 2%, p<0.001), including those with the apical form (64% vs. 30%, p<0.05). Each patient with apical HC had either no or only mild symptoms, and all survived. The morphologic form of nonobstructive HC with hypertrophy limited to the LV apex (apical form of HC) was 5 times more common in an unselected Japanese population. These findings document variability in the phenotypic expression of HC between countries and races, which may be due to differences in environmental factors or genetic background. Patients with the apical form of HC had a benign clinical course.