Allogeneic hematopoieteic stem cell transplantation (HSCT) is the only curative treatment for myelofibrosis (MF), but it is still associated with significant risks and complications. One of these complications is poor graft function, but incidence and risk factors have not been studied yet. We retrospectively studied a cohort of 100 patients with primary MF or post-ET/PV MF who received a reduced-intensity HSCT in our center. The cumulative incidence of primary leukocyte engraftment was 98%. The cumulative incidence of poor graft function was 17% and all of the cases occurred before day 100 after HSCT at a median of 49 days (range 24-99 days). In the univariate analysis, age as continuous parameter (P = 0.05; hazard ratio 1042) and persistence of significant splenomegaly (defined as palpable splenomegaly of ≥ 10 cm under costal margin) at d+30 after HSCT (33% vs 12%; P = 0.05) showed an increased cumulative incidence of poor graft function. In conclusion, the incidence of poor graft function after HSCT for MF is rather high, but did not influence survival. Persistence of splenomegaly after transplantation is a significant factor for poor graft function in myelofibrosis patients. Whether therapeutic reduction of splenomegaly before HSCT would result in a lower incidence of poor graft function should be investigated in future studies.