CASE PRESENTATION: A 32-year-old female was admitted to the internal medicine service after presenting to the ED with myalgias, high grade fever, sore throat and a diffuse erythematous rash. Laboratory studies on admission were significant for pancytopenia and transaminitis. Several hours after admission, she became hypotensive and developed hypoxemic respiratory failure, requiring intubation and mechanical ventilation. A CT scan of the chest showed multifocal lobar consolidations and ground-glass attenuation consistent with ARDS. Empiric antibiotic therapy was started due to concern for septic shock. Infectious work-up including lumbar puncture, echocardiogram, bronchoalveolar lavage (BAL) cultures, and blood cultures were negative. Serum testing for endemic fungal infections, tick-borne illnesses, arthropod-borne illnesses, bartonella, mycoplasma, Parvovirus B19, dengue fever, Q fever, influenza/RSV, HHV6, CMV, syphilis, HIV and hepatitis were negative. However, EBV IgM and IgG were positive and serum EBV PCR measured <2000 copies/mL. Additional laboratory studies were significant for elevated ferritin level (13,664 mcg/L), hypertriglyceridemia (633 mg/dL), elevated lactate dehydrogenase (719 U/L), and elevated serum IL-2 receptors (1828 pg/mL). The patient underwent a bone marrow biopsy. The bone marrow pathology results revealed 70% cellularity with normal maturation, flow and cytogenetics. Hemophagocytosis was present. She was diagnosed with hemophagocytic lymphohistiocytosis secondary to Epstein-Barr Virus infection. Based on this new diagnosis, she was treated with 1g of IV methylprednisolone daily for 3 days, followed by a steroid taper. She improved dramatically and was extubated on hospital day 12. At the time of discharge, the pancytopenia had resolved, and serum ferritin and liver enzymes were downtrending.