A 57-year-old woman with morbid obesity (BMI: 37.39) was scheduled for ligament reconstruction with tendon interposition of the carpometacarpal joint. A difficult supraclavicular brachial plexus block was performed using a 22-gauge regional block needle with a nerve stimulator and 40 ml of 1% mepivacaine. Approximately 10 minutes after the injection, she complained dyspnea, shortness of breath and right mid-thoracic pain. Her oxygen saturation decreased from 100% to 95%. Diagnostic workup revealed right diaphragmatic elevation caused by phrenic nerve block. General anesthesia was induced because of the unsuccessful brachial plexus block and dyspnea with chest pain. She recovered without any residual complications and was discharged on the third postoperative day. Phrenic nerve block is a common complication in supraclavicular brachial plexus block but it is usually not severe and reassurance is enough to control it. However, pre-operative physical conditions that may lead to decreased respiratory reserves, such as morbid obesity should be considered as a risk factors when conducting supraclavicular brachial plexus block.