Introduction: HLH syndrome is a rare but life-threatening condition of severe hyperinflammation caused by uncontrolled proliferation of activated lymphocytes and macrophages secreting high amounts of inflammatory cytokines. It can present in adults as a Sepsis mimic. Case 71-year-old Caucasian male with history of CAD s/p CABG, HTN, HL, colon cancer s/p right hemicolectomy (6 yrs ago) and recent left upper lobe resection for stage 1A lung Cancer was admitted with history of increasing confusion, weakness, diffuse intermittent abdominal discomfort, shortness of breath and hypotension requiring fluid boluses. Symptoms gradually progressed over two weeks and he was transferred to Intensive care unit for persistent hypotension and confusion. Physical exam was remarkable for 8 x 10 cm ulcer with clear base but no erythema or discharge on the right scapular area, and mild basal crackles on chest auscultation. Laboratory exam showed normal white cell count, low platelets of 63, normal electrolytes, creatinine 1.2 mg/dl, AST/ALT 241/98 U, Normal Bilirubin, alkaline phosphatase 593 U, INR of 9.4, low Haptoglobin, fibrinogen less than 50, D-dimer was high at 7.5. CT angio of chest showed no Pulmonary Embolism or infiltrates. He was treated as Sepsis along with disseminated intravascular coagulation(DIC) possibly from abdominal source. Peripheral smear showed burr cells, no schisctocytes, Low platelets. WBC morphology was normal. He required ventilatory support along with two Vasopressors inspite aggressive fluid resuscitation. A CT of abdomen and pelvis did not reveal any source of infection. His Lactate went up to 4.5. Over the next few days, multiple cultures remained negative. Many doses of cryoprecipitate were given to correct DIC. ESR was less than 2, CRP was 0.4. Due to persistent DIC, a Bone Marrow Biopsy was obtained which showed many hemophagocytic histiocytes. His Ferritin was 13085, IL2 receptor 646(normal 45-1100) and triglyceride 245. Based on above findings, the patient was diagnosed with HLH (Hemophagocytic lymphohistiocytosis) syndrome. He was started on etoposide and dexamethasone regimen. He initially responded with less requirements of Vasopressors but later on developed pancytopenia, bacteremia/fungemia not responding to aggressive antimicrobial treatment. Care was withdrawn on day 21 after discussions with family. Discussion Activation and massive proliferation of T cells and macrophages, leads to marked hypercytokinemia, Low natural killer (NK) cell and CD8+ . Presentation in adults is usually associated with malignancies(lymphoma), bacterial(Salmonella, mycobacteria, mycoplasma, rickettsia, legionella, chlamydia), and many viral diseases. Diagnosis in adults is based on 5 out of following 8 criteria(Fever, splenomegaly, cytopenias affecting at least 2 lineages, triglycerides >265, hemophagocytic cells in bone marrow, liver or lymphnode, low or absent NK cells activity, ferritin >500 and elevated sCD25) Diagnosis is often late and difficult as adult patients often do not meet the diagnostic criteria. Current treatment recommendations are based on case series. Most commonly used drug is Etoposide. This syndrome carries a mortality up to 90% in adults. Conclusion HLH should be considered in patients presenting as sepsis with no clear source, very high ferritin, unexplained cypopenia, DIC and normal inflammatory markers.