Thymic tumor is the most common neoplasm originating in the anterior mediastinum. Histologically, thymic tumors and tumorlike conditions have been classified into thymic cyst, thymolipoma, true thymic hyperplasia, thymoma and carcinoid tumor of the thymus gland. We have experienced several tumors and a few tumorlike conditions of the thymus gland in 10 patients: thymoma 6, thymic hyperplasia 2, carcinoid tumor 1 and thymic cyst 1. The age distributions were ranging from 30 to 60 years except for one 3 year old child [malignant thymoma, lymphocytic type], and male to female ratio was 1:1.5. In 6 cases, thymic lesions were removed through lateral thoracic incision [right 2, left 4] because the mediastinal masses were growing far into the pleural space, meanwhile, medially located lesions [4 cases] through median sternotomy incision. Among these 10 patients, 3 were malignant thymomas, in which 2 were died of recurrence after tumor resection. Myasthenia gravis was all noted in 3 females [thymoma 2, thymic follicular hyperplasia 1], in which only two revealed remission in symptoms following thymectomy. The authors would like to recommend early radical thymectomy through median sternotomy incision whenever patients demonstrate suspicious thymic tumor lesions on the chest roentgenogram or generalized myasthenic symptoms. [KTCS 1983;4:571-583]