A 56-year-old postmenopausal woman with a history of colon cancer status after left hemicolectomy presented to our institution with abdominal pain, early satiety, and weight loss. Computerized tomography scan showed a large, enhancing, fat-containing mass displacing the left kidney posteriolaterally suspicious for a retroperitoneal liposarcoma. The lesion was also encasing the renal hilum. The patient underwent a wide excision of the mass as well as a radical nephrectomy and lymph node dissection by means of a thoracoabdominal approach. Final pathology revealed a large lymphatic mass consistent with Castleman's disease.