A 58-year-old woman was admitted due to an abnormal shadow on chest X-ray film and two episodes of hemoptysis during the past two years. Chest radiography showed a mass with calcification in the left upper lobe of the lung. A white polypoid lesion in left B3b + c bronchus was discovered by fiberoptic bronchoscopy. Biopsy specimen of the polypoid lesion demonstrated fungi like aspergilli in the necrotic tissue. We suspected pulmonary aspergillosis combined with old tuberculosis and treated with antifungal and antituberculous drugs. After nine months, however, we recognized that the mass had become larger radiologically. A polypoid tumor with a brown, glossy surface in the left B3 bronchus was again noted endoscopically. Histologic findings of the biopsy specimen obtained from this tumor were suggestive of thymoma. Thymectomy and left upper lobectomy were performed. The cross-section of the surgical specimen revealed that the tumor extended not only in the mediastinum but also in the pulmonary parenchyma with polypoid growth into the lumina of bronchi. Microscopically, the tumor was an invasive thymoma composed of both epithelial and lymphocytic elements.