Fever of unknown origin (FUO) presents a diagnostic challenge. Giant cell arteritis (GCA) may present with FUO and this entity should be included in the differential of elderly patients who present with constitutional symptoms. While a temporal artery biopsy is considered the gold standard for the diagnosis of GCA, a subset of patients with large vessel involvement by GCA may have a negative temporal artery biopsy and no cranial symptoms. We present a 79 year-old woman with FUO and negative temporal artery biopsies in whom diagnosis of GCA was delayed. Further imaging with CT-angiogram and positron emission tomography/computed tomography (PET/CT) scan showed diffuse extensive active vasculitis. The above case underscores the value of imaging studies in the evaluation of patients with FUO from occult large vessel vasculitis.