Hibernoma, a tumor of benign brown adipose tissue can present as a large mass that can mimic a sarcoma. Imaging characterization of large extremity tumors can be very helpful in assessment of these masses for treatment planning and follow-up. We report on a case where FDG-PET imaging was performed on a patient with a large thigh mss, suspected to be a sarcoma. The FDG-PET uptake was highly avid...