Myelolipoma is a rare mesenchymal tumor composed of an admixture of fat and bone marrow-derived hematopoietic cells. It is typically an adrenal lesion, and mediastinal location is extremely unusual. We describe a 56-year-old man with nonspecific symptoms of cough and dyspnea and no underlying disease whose chest computed tomography showed a huge (25 x 15 cm) mediastinal tumor containing calcification. Surgical removal and subsequent pathologic examination of the tumor revealed myelolipoma. Primary myelolipoma should be considered in the differential diagnosis of large posterior mediastinal tumors containing calcification.