We report 2 cases of young patients referred for FDG PET/CT for peripheral lymphadenopathy and moderate fever associated with pericarditis in 1 patient and glomerulonephritis in the other patient. FDG PET/CT showed a very similar appearance in these 2 patients, with highly avid lymph nodes with axillary predominance and diffuse FDG uptake in spleen and bone marrow. Systemic lupus erythematosus with an unusual presentation of generalized lymphadenopathy was diagnosed in both patients. This FDG distribution pattern should be kept in mind when PET is performed for etiological investigation of fever of unknown origin.