We report a case of arrhythmogenic right ventricular cardiomyopathy revealed by sudden death during exercise in a 13-year-old patient. Postmortem diagnosis was made on multiple tissue samples taken from right ventricular free wall, showing light adipous infiltration of the myocardium at gross examination. Arrhythmogenic right ventricular cardiomyopathy is histologically characterized by fibro-fatty replacement of right ventricular myocardium. Left ventricular involvement may be observed. Diagnosis at an early stage is often difficult. Etiology remains unknown. Since familial occurrence has been documented, postmortem identification is useful for the other members of the family.