A 64-year-old woman had intermittent fever for more than a month and was hospitalized. Her initial infectious diagnostic evaluations from chest radiograph, echocardiogram, CT scan of the abdomen, blood culture and urine culture, and bone marrow biopsy were negative. Although the patient began to have a rash several days after admission, her attending doctor did not believe the skin changes were related to her fever. Subsequent F-18 FDG PET revealed multiple foci of intense FDG uptake on the subcutaneous surfaces of back, arms, and thighs. The diagnosis of lobular panniculitis, an inflammatory process of the fat lobules of the subcutaneous tissue, was finally confirmed from skin biopsy.