268 patients (pts) aged between 4 and 63 (average block 33.6) years were examined in an effort to detect structural and/or wall motion abnormalities of the right ventricle, consistent with a diagnosis of Arrhythmogenic Right Ventricular Dysplasia (ARVD). The patients included in this study had some of these features: 1) sudden juvenile death (age less than 35 years) due to heart disease; 2) relatives of pts died suddenly of pathologically proven ARVD; 3) pts with ventricular arrhythmias grade Lown greater than 3, and with QRS morphology mainly of left bundle branch block; 4) pts between the ages of 18 and 40, with negative T waves beyond V2; 5) pts with ventricular arrhythmias of left bundle branch block morphology, and grade Lown greater than 1, and negative T waves beyond V1. ARVD was recognized in 108 living and 18 deceased pts. Our data confirm that ARVD is a wide spectrum disease, going from the classical form described by Marcus and Fontaine to concealed forms characterized mainly by premature ventricular complexes.