We report 2 rare cases of extraskeletal Ewing's sarcoma, one is arising primarily from the posterior mediastinum in a middle-aged man (patient 1), and the other one is arising from the left kidney in a young male patient (patient 2). The CT in the first case showed a large mass of heterogeneous texture, with areas of cystic changes in the right side of the posterior mediastinum, no underlying bony changes or intra-spinal extension, and this mass was diagnosed as lymphoma. The second case showed almost complete replacement of the left kidney by a mass with extension through the renal vein and inferior vena cava, and it was diagnosed as renal cell carcinoma. The histological analysis of these lesions revealed extraskeletal Ewing's sarcoma.