Background Several morphologic distinctions between elderly and young patients with hypertrophic cardiomyopathy (HCM) have been reported. In particular, a crescent-shaped left ventricular (LV) cavity with reversed septal curvature, which is often seen in young patients, is rare in elderly patients. However, those studies were carried out before gene testing became available and heterogeneous causes or age-related changes may have been included. The purpose of this study was to determine the morphologic characteristics of elderly patients with HCM definitely caused by a mutation in the cardiac myosin-binding protein C (MyBPC). Methods and Results Twenty-seven patients with HCM caused by MyBPC gene abnormality were evaluated. Patients were divided into an elderly group (≥65 years of age, n=8) and a young group (<65 years of age, n=19). LV hypertrophy was milder in the elderly than in the young for maximum LV wall thickness (18±5 mm vs 24±6 mm, p=0.008) and Wigle score (5.7±1.5 vs 7.6±1.6, p<0.005). However, an abnormal crescent-shaped LV was similarly prominent in both groups (75% in the elderly vs 95% in the young, p=NS). None of the elderly patients showed a proximal septal bulge. Conclusions An abnormal crescent-shaped LV cavity was frequently present in the elderly as in the young when there are MyBPC mutations. It is possible that this morphologic feature could become useful for determining the etiology of HCM in elderly patients. (Circ J 2006; 70: 875 - 879)