The pure retroperitoneal lipoma is a sporadic benign tumor originating from the mesenchymal tissue. There are only a few data in the literature. The technique available at this moment cannot establish a clear distinction between a benign adipose mass and a low-grade liposarcoma. This study presents the case of a 53-year-old man presenting computed tomography (CT) and magnetic resonance imaging (MRI) findings that revealed a giant retroperitoneal fatty tumor of 365∕210∕165 mm dimensions, suspected of malignancy. The patient's medical history, clinical data, and blood tests are more likely inclined to a benign condition. Liposarcoma couldn't be excluded preoperatively. The patient underwent an open surgical procedure respecting the oncological principles, with complete resection of 6400 g of retroperitoneal adipose tumor that also affected the surrounding organs' normal abdominal anatomy. The tumor was relatively well delimited without any signs of local invasion or infiltration. Three solid masses described on the MRI were identified upon dissection and sent separately for histological examination. The result indicated a giant retroperitoneal lipoma with benign characteristics. Facing imagistic difficulties to distinguish lipoma from liposarcoma clearly, and the inconclusiveness of fine-needle biopsies, oncological resection remains the only option as a diagnostic method and curative treatment.