Abstract： Objective To probe into the role of hemophagocytosis in bone marrow in the diagnosis and treatment of hemophagocytic lymphohistiocytosis(HLH).Methods The results of the bone marrow smear of patients confirmed with HLH in pediatric department from December 2003 to December 2009 were retrospectively reviewed,and the clinical data of patients hospitalized in the same period being identified with hemophagocytosis but excluded HLH were analysed.The diagnostic criteria were according to the HLH-2004 protocol.Results ① 61 patients were diagnosed with HLH,among them 56 patients had hemophagocytosis in their initial bone marrow smear,while 3 patients had no hematophagocyte in their first bone marrow aspiration,but after 2 ～4times recheckment during the next 2 ～ 3 weeks,these three patients had positive bone marrow results.2 patients had no hematophagocyte throughout.②14 patients excluded HLH revealed hemophagocytosis in their bone marrow,and all these patients recovered after anti-infective and symptomatic treatment.Conclusion Hemophagocytosis in bone marrow is not necessary for the diagnosis of HLH,confirming that a bone marrow lacking hemophagocytosis does not rule out the diagnosis of HLH,and a negative initial bone marrow aspiration should not delay crucial treatment.Reviewing bone marrow is instructional during the course of treatment.For another,diagnosis only according to the positive findings in bone marrow is wrong.