Post allogenic hematopoietic cell transplant (HCT) hemophagocytic lymphohistiocytosis (HLH) is an aggressive disease with unknown etiology. It has a poorly understood pathophysiology and poor outcome if untreated early. It's a state of hypercytokinemia. There are many proposed diagnostic criteria for Post HCT HLH. It usually occurs early in the first 2-6 weeks after allogeneic HCT but can present late. The incidence is highest among cord blood transplant compared with other sources of stem cells with a higher incidence in HLA mismatch donors. Post HCT HLH has a marked low survival rate, when compared with Non-HLH post HCT patients and specifically poor outcome is associated in patients with liver dysfunction, graft failure, and those with endothelial complications. Steroid is the mainstay treatment which can be followed up by cyclosporine and etoposide though an optimal therapy is not known. Intravenous immunoglobulin (IVIg) has been tried in virus associated HLH. Second bone marrow transplant is a rescue procedure in patient with HLH due to graft failure, though a very careful selection of individual patients is mandatory. It has been recently found that etoposide based conditioning regimen may reduce HLH post HCT. A prospective study on post HCT HLH are needed to evaluate this unrecognized condition.