Hibernoma is a rare benign tumor of soft tissue, composed of brown fat. This tissue is predominant in hibernating animals and hence its name. Because of its rarity in Pediatrics and difficult diagnosis, we report a 3 month-old patient with a diagnosis consistent with an abdominal tumor. Ultrasound and computed tomography exams showed an infiltrative retroperitoneal tumor, with hypervascular and lipomatous features. After tumor excision, histopathological exam confirmed the diagnosis of hibernoma or brown fat tumor. This presentation describes the characteristics of this type of tumor, rare in children, and reviews the fatty tumors, according to their frequency in pediatric patients.