A 33-year old man underwent an F-FDG PET/CT searching for the cause of a fever of unknown origin. F-FDG PET/CT incidentally detected a focal area of markedly increased radiopharmaceutical uptake corresponding to a 2.5-cm nodule in the right adrenal gland. Laboratory data ruled out the presence of a functioning adrenal lesion. All these findings were suggestive of adrenal malignancy. After right adrenalectomy, histology showed a benign solitary fibrous tumor of the adrenal gland. This case highlights that benign solitary fibrous tumor should be considered as possible false-positive F-FDG PET/CT finding for malignancy in evaluating adrenal incidentalomas.