A 55-year-old woman had progressive lower extremity weakness. She had an 80-pack-per-year history of cigarette smoking. Electromyographic findings were consistent with the Lambert-Eaton myasthenic syndrome. Despite a normal chest x-ray, normal laboratory studies, and negative bronchoscopy, investigation for lung cancer was pursued. The final thoracotomy and pathology reports indicated a diagnosis of oat cell carcinoma. After treatment with chemotherapy and radiation therapy, clinical and electrophysiologic findings have resolved. Two years after diagnosis, the patient remains in good health without evidence of recurrence.