An active, healthy, and symptom free 16 year old boy with a family history of hypertrophic cardiomyopathy died suddenly while walking home from school. Necropsy showed absence of left ventricular hypertrophy (that is, normal heart weight), though the characteristic histological abnormalities of hypertrophic cardiomyopathy, such as cardiac muscle cell disorganisation and abnormal intramural coronary arteries, were present. It is likely that this patient had hypertrophic cardiomyopathy and died before left ventricular hypertrophy developed.