Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening extreme whole body inflammatory state. It results from the pathological hyperactivation of the immune system, because of congenital or acquired abnormalities of cytotoxicity and NK or T cells. Uncontrolled stimulation of lymphocytes and macrophages lead to hypercytokinemia, organ infiltration by these cells and multiple organ failure. There are genetic HLH and secondary HLH, associated with infections, autoimmune disorders, malignancies. The frequency of the secondary form is difficult to estimate because of the wrong and difficult diagosis. The clinical course is often insidious and nonspecific. Symptoms are varied. The most important are: unremitting fever, hepatosplenomegaly. Generalized edema, rash, lymphadenopathy may occur. Liver failure, respiratory, circulatory and multiple organ failure could develop in a very short time. Most common abnormalities in additional tests are: cytopenias, hypofibrinogenaemia, hypertriglyceridaemia, hyperferritinaemia, hypertransaminasaemia, elevated parameters of inflammation (excepting lowering erythrocyte sedimentaion rate). Criteria for diagnosis and therapeutic protocols referto the genetic forms of HLH. Currently, there are no guidelines for secondary HLH. Diagnostic and therapeutic difficulties also arise from clinical picture, similar as in the systemic inflammatory response syndrome, sepsis, multiple organ dysfunction syndrome. We present the clinical presentation, diagnostic pitfalls and treatment of secondary HLH, based on a review of the current literature and our own observations.