We experienced a complication of brachial plexus palsy secondary to operative position during thoracoscopic thoracic sympathectomies. His general health was excellent and no previous histories vulnerable to peripheral nerve systems were observed. The thoracic sympathectomies were done under general anesthesia. The patient was placed left lateral position with his right arm abduced 150o on padded arm board. An operation was lasted 2 hours and 30 minutes at this position because of severe right apical lung adhesion. The controlateral side was performed same procedure and lasted 20 minutes. After the patient recovered from the anesthesia, the patient had a complete paralysis of right arm. There was also slightly diminished sensation to pinprick on the arm and hand. Neurologic examination and EMG study revealed brachial plexus palsy. Nerve blocks and physiotherapy were performed to treat brachial plexus injuries. His motor functions were improved day by day and he was discharged with a complete range of motion against gravity on 14th. postoperation day. However, there were loss of muscle powers against some resistances and tingling sensations of fingertips. Two months later, he was recovered completely and there was no residual disabilities.