Fifteen patients with right ventricular tachycardia without evidence of coronary artery disease or dilated or hypertrophic cardiomyopathy were evaluated, by means of electrophysiologic study and right ventricular endomyocardial biopsy. Six cases were diagnosed as definite arrhythmogenic right ventricular dysplasia (ARVD), while 2 cases without characteristic findings of ARVD by noninvasive studies and angiography were diagnosed as probable ARVD on the basis of their electrophysiologic and histopathologic data. In conclusion, ARVD is relatively common as an etiology of right ventricular tachycardia, and detailed electrophysiologic study and endomyocardial biopsy appear to be useful for diagnosis of ARVD.