The relationship between myasthenia gravis and thymic pathology, including thymoma, is well known. Approximately 10% to 15% of patients who have myasthenia gravis are observed to have a thymoma. Myasthenia gravis may be considered as the most common of the paraneoplastic syndromes in patients who have thymoma. This article summarizes the clinical aspects of myasthenia gravis, followed by a review of the less often recognized paraneoplastic disorders noted to occur in patients who have thymoma.