The brachial plexus is formed by union of C5, C6, C7, C8 and T1 root levels. Bachial plexus injuries can be categorized by ther causative mechanism as gunshot injuries, sharp injuries, traction injuries, motor accidents and radiation. The objective of the present study is to show the risk of interscalenic block as permanent lesion of brachial plexus in arthroscopic acromioplasty surgery. We present a 35 years old female administration worker. She was sent from second level unit with subacromial impingement diagnosis. At the moment of surgery the patient presented incomplete sensitive block, so general anesthesia was performed. At the next day the patient had a numb arm, difficulty in mobilization with no edema. She was re-evaluated by anesthesiology the next day, and they thought of prolonged action of the anesthetic used (bupivacaine). An electromyography was performed and it reported moderate axonal plexopathy, with affection of superior trunk and lateral cord. We must take into account the possibility of lesion of brachial plexus by interscalenic block and not by arthroscopic surgery.