The brachial plexus block by interscalene approach is useful for any procedure on upper extremity, including the shoulder. Complications such as high epidural block, total spinal anesthesia, permanent neurologic damage, phrenic nerve block, cardiac arrest, pneumothorax and Horner's syndrome etc. were reported. Ipsilateral Horner' syndrome can be used for confirmation of the accompanying sympathetic block. We experienced a case of 35-year old male patient who developed ipsilateral Horner's syndrome following the injection of 40ml of 1% lidocaine with 1 : 200,000 epinephrine to brachial plexus by interscalene approach. This compication lasted for 10days after interscalene brachial plexus block.