Abstract: AIM To determine the value of several surface electrocardiographic criteria for differentiating origins of right outflow tract ventricular arrhythmias. METHODS The present investigation studied ventricular arrhythmias in 139 patients who underwent successful catheter ablation in the right ventricular outflow tract (septal, n=111; free wall, n=28). Several electrocardiographic criteria including morphology of QRS in lead I, QRS duration, transitional zone in precordial leads and notch on R wave in inferior limb leads were used to judge the origin. RESULTS An R-wave duration ≥ 140 ms for predicting the origin from free wall had a sensitivity of 86% and specificity of 58%. Notch on the R-wave in inferior limb leads had a sensitivity of 64% and specificity of 91%. An R-wave in lead I had a sensitivity of 86% and specificity of 73%. CONCLUSION The morphology of QRS in lead I and the notch on R wave in inferior limb leads can accurately differentiate free wall from septal sites of right ventricular arrhythmia origins. These results potentially may be of significant value for guiding catheter ablation.