We treated a 42-year-old man with pulmonary tuberculosis presenting as a round mass in a cavitary lesion that resembled a fungus ball. These findings appeared within a short time. The diagnosis was confirmed by isolation of Mycobacterium tuberculosis from his sputum. He also had diabetes mellitus that was poorly controlled. The patient was treated with antituberculous chemotherapy and insulin therapy. With these treatments, the roentgenographic abnormalities resolved fairly rapidly.