One hundred five patients with an accessory atrioventricular pathway underwent catheter ablation of the pathway using radiofrequency current. There were 79 accessory pathways located on the left and 32 on the right side of the heart. In patients with right-sided pathways ablation was attempted via a catheter positioned at the atrial aspect of the tricuspid annulus. In patients with a left-sided free-wall accessory pathway a novel approach was utilized in which the ablation catheter was positioned in the left ventricle directly below the mitral annulus. Accessory pathway conduction was permanently abolished in 93 patients (89%). Failures were mainly due to inadequate catheters used initially. It is concluded that catheter ablation of accessory atrioventricular pathways using radiofrequency current is an effective and safe therapeutic modality for patients with symptomatic tachyarrhythmias mediated by these pathways.