Pancoast tumor is a specific lung carcinoma that has symptoms according to the location. It often involves the extrathoracic structure more than parenchyme of lung, that cause shoulder pain. A 61-years old man had been complaining of shoulder pain and limitation of range of motions of shoulder joint. Conservative management of the shoulder pain was not effective with physical therapy and injection therapy and the symptom of right upper extremity radiating pain had been aggravated. We had examination of the eletro-diagnostic test in 17 months after shoulder pain was developed. The findngs of the electrodiagnostic test was suspected as the injury of lower trunk of brachial plexus, so we had checked MRI on brachial view. The pancoast tumor was found in the extrathoracic region that invaded the lower trunk of the brachial plexus. The shoulder pain related with tumor was rare and could cause brachial plexopathy. (J Korean Acad Rehab Med 2005; 29: 149-153)
