This prospective study enrolls subjects who have clinical and laboratory manifestations related with hemophagocytic lymphohistiocytosis. The purpose of the study is to evaluate clinical and biological features of adult hemophagocytic lymphohistiocytosis. The enrolled subjects into this study will be evaluated according to the HLH (hemophagocytic lymphohistiocytosis)criteria and treated with systemic immunosuppressive therapy or chemotherapy. All subjects will be regularly monitored by physicians participating in this study.