In myelofibrosis, the introduction of reduced- intensity conditioning (RIC) preceding allogeneic stem cell transplantation (SCT) resulted in lower transplant- related mortality rates compared with myeloablative conditioning. However, lowering the intensity of conditioning may increase the risk of graft failure in myelofibrosis, although hitherto this has not been indisputably proven. We here report the outcome of 53 patients who underwent allogeneic SCT with different conditioning regimens (RIC and nonmyeloablative (NMA)) in three transplantation centers in the Netherlands. The cumulative incidence of graft failure within 60 days after SCT was high (28%), and this was primarily associated with the intensity of the conditioning regimen. Cumulative neutrophil engraftment at 60 days was lower in patients who received NMA conditioning compared with those who received RIC (56% vs 84%, P = 0.03). Furthermore, of six patients who received a second transplantation after graft failure, the three patients with RIC regimens subsequently engrafted, whereas the three patients who received a second NMA regimen did not. This study indicates that in myelofibrosis, NMA regimens result in high engraftment failure rates. We propose the use of more intensive conditioning regimens, incorporating busulfan or melphalan.