Assessing 100 cases of arrhythmogenic right ventricular dysplasia causing unexpected sudden death, we stress two aspects of the disease, specially concerning pathologists: diagnosis value and limitations of endomyocardial biopsy and high frequency of the disease among unexpected sudden death in young adults. When the disease is identified genetic screening should be performed among patient's family members. The anterior right ventricular wall is very thin (partly or completely) and microscopic examination shows absence of muscle cells, replaced by normal fatty tissue. Associated lesions are often present: slight abnormalities of left ventricle, mucoid degeneration of auriculo-ventricular valves and recently described lesions of His conductive tissue. Apoptotic anomalies are now incriminated for agenesy or disappearing right ventricular muscle.