The histopathology, clinical features, treatment, and results are reported in twenty-nine patients with thymoma. Benign and malignant thymomas are differentiated by their invasive characteristics. Surgical excision is recommended for benign lesions. Surgical excision and postoperative irradiation are recommended for malignant thymomas irrespective of the predominant cell type. The recommended treatment for thymoma and the symptomatic results in myasthenia gravis are unpredictable.