Recently, Yamakawa et al. following Masaoka's clinical staging of thymic epithelial tumors, proposed a TNM classification and staging system for thymic epithelial tumors including thymoma and thymic carcinoma. The present authors consider that division of thymomas into circumscribed types (either encapsulated or non-encapsulated but confined to within the thymus) and those invasive to adjacent organs or structures is sufficiently practical, and that a staging system is applicable to thymic carcinoma, carcinoid tumors and germ cell tumors of the anterior mediastinum, which are more malignant than thymoma. Therefore, the utility of the Yamakawa/Masaoka TNM and staging system was evaluated and a modification proposed based on experience with 16 thymic carcinomas. Although there were no cases at stage II, the survival curves obtained using the proposed modified system were more clearly separated between stages I and III or IV and between stages III and IV than the curves obtained using the Yamakawa/Masaoka system. However, the differences were not significant because of the small number of cases included. A statistically significant difference was noted between the survival curves for patients who underwent complete and incomplete surgical resection of the tumor. The utility of this proposed TNM and staging system must be evaluated by other investigators, since no cases of small cell carcinoma, lymphoepithelioma-like carcinoma, sarcomatoid carcinoma and clear cell carcinoma were included in this series, all of which are considered to have high-grade histology. An evaluation of carcinoid tumor and germ cell tumor of the anterior mediastinum must also be made.