From 1983 to 1988, 51 patients with the Wolff-Parkinson-White syndrome underwent surgical ablation of an accessory conduction pathway, 25 by the classic endocardial approach and 26 by the epicardial technique supplemented by cryosurgery. In the endocardial and epicardial groups, the accessory pathway was in the left free wall in 22 and 18 patients, respectively, posterior septal in two and seven, and in the right free wall in one patient in each group. There was no early or late death in the endocardial group, and postoperative complications developed in five patients (20%). Pathway ablation was completely successful in 22 patients (88%), preexcitation recurred in two patients (8%), and one had recurrence of supraventricular tachycardia (4%). One of the failures occurred with a posterior septal pathway (50%), and the two others with a left free-wall pathway (9%). With the epicardial technique, there were no early deaths and one late death caused by atherosclerotic coronary artery disease. Five patients (19%) had postoperative complications. The pathway was ablated successfully in 22 patients (85%), preexcitation recurred in three patients (12%), and supraventricular tachycardia remained inducible in another patient despite disappearance of the delta wave. Three of those failures occurred with anterior left free-wall pathways (16%), but only one patient had recurrent supraventricular tachycardia (4%) requiring immediate reoperation, which was successful. In conclusion, although epicardial or endocardial approaches produced similar results, our observations suggest that left free-wall accessory pathways located high anteriorly may be ablated in a more reproducible way with the endocardial technique, whereas the epicardial approach appears easier for posterior septal pathways. We therefore believe that any surgeon beginning such surgery should be aware of the possibilities and limitations of each of the two techniques.