DISCUSSION: HLH can be suspected based on criteria from HLH-2004 guidelines which include molecular identification of HLH-associated genes or at least 5 of 8 criteria: Fever ≥ 38.5 C, splenomegaly, two peripheral blood cytopenias, hypertriglyceridemia or hypofibrinoginemia, hemophagocytosis in the bone marrow, low NK cell activity, ferritin > 500ng/mL, and sCD25 count ≥ 2400/mL. Initially, our patient met 5 of 8 criteria but they were thought to be non-specific. While the diagnosis of HLH was still entertained, other etiologies for her FUO were also considered. However, the results of the PET were instrumental in the decision to obtain the outside bone marrow slides. While hemophagocytosis was not initially reported, it was identified on secondary review confirming the diagnosis.