BACKGROUND: Intercostal nerve damage is often suggested to be the cause of pain after thoracotomy. METHODS: This was a prospective randomized study of 120 patients who had posterolateral thoracotomy. They were equally divided into two groups, the first in which intercostal muscle flap and intracostal sutures were used, and the other group in which the usual pericostal sutures were used. These two groups were compared regarding operative time, rib fracture, postoperative pulmonary functions, time to ambulation, pain score in the first week, doses of analgesics injected in the epidural catheter, postoperative complications, chest tube drainage, hospital stay, return to daily activities, and pain score and use of analgesics at 1, 3, and 6 months. RESULTS: Postoperative pain score throughout the first week was significantly lower in the patients in the intercostal muscle flap group, who had also a significantly earlier postoperative ambulation and return to normal daily activities, and received significantly lower doses of postoperative analgesics. After 1 month, patients in the intercostal muscle flap group had a significantly lower pain score and use of analgesics. After 3 months, pain score was not significantly different between both groups, but the use of analgesics was significantly lower in the intercostal muscle flap group. After 6 months, no significant difference was present between both groups with regard to pain score or the use of analgesics. CONCLUSIONS: Intercostals muscle flap and intracostal sutures are rapid, safe, and effective procedures in decreasing early pain after thoracotomy with subsequent earlier return to normal daily activities and lesser use of analgesics.