Hemophagocytic Lymphohistiocytosis (HLH) is very rare in adults but can be fatal without treatment. Reports in adults are limited to case reports and very small case series. Clinically it is characterized by fever, hepatosplenomegaly, lymphadenopathy, severe cytopenias, hepatic dysfunction, coagulopathy, as well as neurological involvement. This syndrome is associated with diverse processes including: infection, rheumatologic, and hematologic malignancies. Presently, the underlying cause of HLH is unknown. We present a cosecutive series of 10 adults with HLH diagnosed at our institution between 2004–2006. All diagnoses were confirmed by pathology. The median age was 59 years (range: 18–73 years), and a male: female ratio of 4:1. All patients uniformly presented with fever. Half of the patients presented with evidence of hepatomegaly or splenomegaly. The most predominant laboratory abnormalities included: leukopenia or thrombocytopenia (100%), and elevation of liver enzymes (50%). EBV IgG was positive in 8 of 10 patients. The underline illnesses associated with HLH were diverse. The underlying causes were as follows; acute leukemia (n=2), infection (n=2), rheumatologic (n=2), post transplant (n=2) sickle cell disease (n=2), unknown (n=2). Mortality rate was 60% with a median survival time since diagnosis of 58 days. One patient is still on maintenance cyclosporin after etoposide treatment. One patient is on steroid and cytoxan. One patient recovered just with supportive care. In conclusion, due to the high morality rate associated with HLH, early treatment with immunosuppressant is warranted and attempts to identify underlying cause.