We report here a case of thymoma simultaneously associated with undifferentiated pleomorphic sarcoma. A 45-year-old male presented with axillary lump. Radiographic studies showed a mediastinal mass. On fine needle aspiration cytology and histopathological examination, a diagnosis of thymoma with coexisting undifferentiated pleomorphic sarcoma was made. Although thymomas are associated with many extrathymic malignancies, it's association with undifferentiated pleomorphic sarcoma is rare. This case is being reported on to reinforce that clinicians should bear in mind the possibility of extrathymic malignancies in patients with thymomas.