The pre- and intraoperative electrophysiological studies in 9 patients with two or more accessory pathways are described. The presence of multiple accessory pathways was clinically suspected in only 2 patients. During the preoperative electrophysiological study two accessory pathways were identified in 7 patients and a single pathway in 2 patients. At operation, additionally three accessory pathways were identified in 3 patients. One out of two pathways, found preoperatively, could not be confirmed in 1 patient. It is concluded that the clinical or preoperative electrophysiological evidence of only one accessory pathway should not distract one’s attention from considering multiple accessory pathways in patients presenting only one type of tachycardia.