Hemophagocytic syndrome results from a inappropriate stimulation of macrophages in bone marrow and lymphoid organs, leading to phagocytosis of blood cells and production of high amounts of pro-inflammatory cytokines. This life-threatening disease combines non-specific clinical signs (fever, cachexia, hepatomegaly, enlargement of spleen and lymph nodes) as well as typical laboratory findings (bi- or pancytopenia, abnormal hepatic tests, hypofibrinemia, elevation of serum LDH, ferritinemia and triglyceride levels). Diagnosis is confirmed by cytological or pathological examination of bone marrow or tissue specimens. Hemophagocytosis may be primitive, essentially in pediatric population, or secondary, related to various situations such as lymphomas, infections (viral, bacterial or parasitic) or auto-immune diseases. Prognosis is poor, depending on the associated disease, with an overall mortality of 50%.Recent advances, essentially due to genetic studies of familial hemophagocytic syndrome, have underlined the major role of T lymphocytes and TNF alpha in the pathogenesis of hemophagocytosis. In these pediatric cases, prognosis has dramatically improved since allogenic bone marrow transplantation is performed, raising long-term survival from 10 to 66%.In secondary forms of hemophagocytic syndrome, treatment must be symptomatic (transfusion, correction of electrolyte disorders) and etiological (chemotherapy, anti-viral or antibiotic drugs, immunosuppressive therapy). However, prospective trials are necessary to define the best treatment in these cases. New therapeutic options, targeting specific mediators, including TNF alpha, may emerge with the understanding of pathogenesis of hemophagocytic syndrome.