Primary retroperitoneal tumors are relatively rare and the histological characters vary. We present the case of a retroperitoneal lipoma in a 51-year-old male patient, whose main complain was enlarging of the abdomen in the last 2 months. The CT of the abdomen and pelvis revealed a giant retroperitoneal tumor. The patient suffered a surgical intervention that revealed a giant retroperitoneal tumor, 40/35 cm, weighting 14 Kg. The pathology exam established the diagnosis: retroperitoneal lipoma with areas of necrosis and lipogranulomatosis. The postoperative evolution was simple.