Failure to engraft after hematopoietic stem cell transplantation (graft dysfunction) or to sustain engraftment (graft rejection) is a formidable complication due to many possible factors. These include inadequate stem cell numbers, infections, graft-versus-host disease and immunological mediated processes. Fortunately, this complication is uncommon and can be overcome by additional hematopoietic stem cell infusions. Multiple treatment alternatives have been explored including hematopoietic growth factors, additional infusions of stem cells alone, with augmented immunosuppression or with additional cytotoxic therapy. Various sources of the additional stem cells are feasible including the original donor, using another donor, using stem cells collected from the marrow or after cytokine mobilization from the peripheral blood. This report will overview this complication and review the various studies that have attempted to define both cause and therapy. However, a lack of well-designed prospective studies has made definitive recommendations difficult although basic principles have been established.