A lymphatic system disease that is characterized by an expansion of the monocyte-macrophage population and intense hemophagocytosis. It can occur de novo, but more often occurs in the setting of another disorder, usually an infection or a malignancy. A clinical picture of fever, hepatosplenomegaly, lymphadenopathy and peripheral pancytopenia. The morphologic hallmark of this syndrome is the phagocytosis of hematopoietic elements by morphologically normal macrophages.