We report a case of thymoma simultaneously associated with two hard masses of large diameter measuring about 9 cm. A 66-year-old male presented with a cough. Radiographic studies showed a mediastinal mass. Fine needle aspiration cytology and histopathological examination confirmed a diagnosis of thymoma with a coexisting undifferentiated pleomorphic sarcoma. Thymomas are associated with many extrathymic malignancies. Two hard masses were found on either side of the midline; the greatest diameter of the right mass measured 9cm and the left 8.5 cm. The mass on the right of the midline had loosely adhered to the anterior pericardium, the right subclavian vein, the cava vena superior and the anonymous vein.