Hemophagocytic syndromes are the clinicobiological translation of an unconnected macrophagic activity with hemophagocytosis. Their physiopathology is related with a deregulation of the T lymphocytes and an excessive production of cytokines. Acquired hemophagocytic syndromes are mostly associated with underlying pathology which they can reveal: immunodeficiency, infections (mostly of viral origin), hemopathies and cancers, auto-immune diseases. The main clinicobiological features are fever, hepatosplenomegaly and peripheric bicytopeny. In the majority of cases, the diagnosis is confirmed by a myelogram which shows the presence of benign histiocytes, actively phagocyting the hematopoietic cells. The pejorative prognosis of hemophagocytic syndromes (actual mortality rate 30 to 45%) requires an early therapy which associates etiological treatment of the underlying affection with pathogenic treatment (pulse of corticosteroids, immunoglobulins, immunosuppressors, or plasmapheresis).