Introduction: Although Task Force Criteria for arrhythmogenic right ventricular dysplasia (ARVD) include fibrofatty infiltration of myocardium as one of major diagnostic criteria, the clinical implication of endomyocardial biopsy (EMB) for the diagnosis of ARVD is not known well. Method: Since 2001, 51 patients who showed nonischemic wall motion abnormality with and without ventricular arrhythmia were studied with routine ECG, 2-D echo, exercise ECG, Holter ECG, SAECG, coronary angiography, right and left ventriculography and EMB. Biopsies were performed from the right side of interventricular septum with a 5.5 F or 7 F biopsy forcep (Cordis, USA). Biopsy was guided with both fluoroscopy and 2-D echo. Two to six samples (2 to 3 mm in diameter) obtained from each patient were processed and stained with HE, trichrome, PAS and LCA. Results: Task Force Criteria for ARVD were met in 22 patients in which 3 patients with typical features of dilated cardiomyopathy on EMB were excluded. Finally 19 patients (12 females, mean 44짹13 years old) were included. Their symptoms were cardiac arrest in 1, syncope in 4, palpitation in 6, atypical chest pain in 3, heart failure in 1, sudden death of brother due to ARVD in 1 and no symptom in 3. Histology was diagnostic for ARVD in 16 (84%) patients and normal or nonspecific in 3 (16%). Diagnosis might not be possible in 6 (32%) patients if biopsy finding was not diagnostic for ARVD. No complications related to EMB occurred in our patients except one case of right bundle branch block. Conclusion: Extensive studies including EMB may be needed for the proper diagnosis of ARVD.