Hypertrophic cardiomyopathy (HCM) is a heterogeneous disease, characterized by asymmetric hypertrophy of the left and/or right ventricle with disarray of myocardial fibers. In order to know its clinical and electrocardiographic manifestation in the pediatric age group, we made a retrospective study of 24 cases from 1986 to 1995. There were: 15 girls and 9 boys, with a mean age of 6 years (age range: 1 month to 17 years). Clinical manifestations were dyspnea (71%), syncope (42%) and palpitations (42%). Physical examination disclosed an aortic systolic murmur in all patients, a mitral regurgitation in 42% and physical signs of congestive heart failure in 54% of patients. Chest X rays showed cardiac enlargement in 71% and pulmonary capillary hypertension in 42%. The most frequent ECG abnormalities were: a prolonged time in the intrinsecoid deflection onset on leads corresponding to the affected region, more or less deep and clean Q waves on leads aVF, aVL, V5 and V6, as well as supraventricular and ventricular rhythm disturbances in 11 patients (46%) with and without congestive heart failure. Bidimensional echocardiography confirmed antero-septal hypertrophy in all patients. The mortality rate was 17%. HCM is rare disease in the pediatric age group. Mortality increases when congestive heart failure and arrhythmias are present. Treatment must be individualized in all cases.