BACKGROUND: Cryoanalgesia provides postoperative analgesia following thoracotomy without serious complications compared with epidural analgesia, but little data indicates which one is better in terms of postoperative analgesia, side effects or associated complications. METHODS: Forty patients undergoing lateral thoracotomy, were randomized to receive a mixture of fentanyl and 0.15% bupivacaine at 0.5 microgram/kg/h of fentanyl via thoracic epidural catheter (Group E) or cryotherapy on the 4th, 5th, 6th, or 7th intercostal nerves using Frigitronics (Group C). Postoperative pain was assessed everyday for 7 days after the thoracotomy by a visual analog scale (VAS). The side effects and patient satisfaction of analgesia were assessed by a system of 4 grades. RESULTS: The VAS scores at rest in group C were significantly higher than those in group E. There was no side effect except numbness in group C, which continued for 3 months on the average. The incidences of side effects (nausea, vomiting, pruritus, sedation, urinary retention) were 15-35% in group E. The 35% of patients in group C were satisfied with postoperative analgesia compared with 95% in group E (P < 0.05). CONCLUSIONS: Epidural fentanyl provided a better analgesic effect than cryoanalgesia for thoracotomy, but there is a clinical advantage in cryoanalgesia over epidural fentanyl with respect to incidences of serious side effects not including. (Korean J Anesthesiol 2000; 39: 83-90)