['The management of postthoracotomy pain is a problem and may contribute to atelectasis, leading to hypoxemia, pulmonary infection, and permanent alveolar damage. We sought to determine the efficacy of interpleural analgesia for pain control and to evaluate independent predictors for postoperative pain intensity. Eighty-three patients undergoing elective anterolateral (n = 37) and posterolateral (n = 46) thoracotomy were included in a prospective, randomized, double-blinded trial. Patients were assigned to receive either 0.5% bupivacaine or saline solution interpleurally every 4 h for 10 doses postoperatively. All patients also received patient-controlled analgesics (PCA) with piritramide as the opioid for additional pain control. Pain was assessed on the basis of PCA requirements and by using a visual analog scale. Visual analog scale scores and PCA requirements were not different between groups. Both interpleural bupivacaine and saline significantly reduced pain scores 30 min after the administration. We concluded that pain reduction by interpleural instillation of bupivacaine reflects a placebo-like effect; however, interpleural analgesia is not effective in patients undergoing lateral thoracotomy. Sex and surgical approach were shown to influence postoperative pain intensity at rest, but not during coughing. The female patients, and those undergoing posterolateral thoracotomy, exhibited higher pain scores. This observation appears to be of only marginal clinical significance. The efficacy of interpleural analgesia to reduce postoperative pain intensity in patients after lateral thoracotomy is controversial. In this study we demonstrated a lack of efficacy of interpleural analgesia.'] Does interpleural analgesia influence postthoracotomy pain?