Thoracic epidural analgesia is a common method of pain relief for thoracic and upper abdominal surgery. Misplacement of the epidural catheter is one of the complications associated with epidural analgesia. A 60-year-old man was scheduled for a right pneumonectomy under general anesthesia. Before inducing general anesthesia, the patient was placed in the left lateral decubitus position. A 18-gauge Tuohy needle was inserted into the T6-T7 level using the left paramedian approach 1.5 cm lateral to the midline with a loss of resistance at 7 cm, and uneventful catheter advancement was performed. Approximately 30 minutes after commencing surgery, the surgeon found the epidural catheter in the right pleural cavity. We report a case of the accidental intrapleural positioning of a thoracic epidural catheter.