Hemophagocytic syndrome (HPS) is a rare immune disease and a potentially life-threatening disorder characterized by cytokine storm and overwhelming inflammation causing fever, hepatosplenomegaly, cytopenia, hypertriglyceridemia, hyperferritinemia, and hemophagocytosis in bone marrow, liver, spleen or lymph nodes. It can be either primary due to a genetic defect (primary hemophagocytic lymphohistiocytosis), or secondary to malignancies, to infections, most commonly with viruses such as Epstein-Barr virus or cytomegalovirus, human immunodeficiency virus, or to autoimmune disorders such as systemic lupus erythematosus or adult-onset Still disease (secondary hemophagocytic lymphohistiocytosis). The disease is hemophagocytic syndrome (MONDO_0015540, a Monarch Disease Ontology id). Also known as: HLH, Hemophagocytic Lymphohistiocytosis, hemophagocytic lymphohistiocytosis.