Fifty-one patients with primary myelofibrosis (PMF) received allogeneic haematopoietic stem cell transplants from related (n ¼ 33) or unrelated (n ¼ 18) donors. Twenty-seven patients, 19-54 years old, were prepared with myeloablative regimens including CY plus BU (n ¼ 4) or TBI (n ¼ 23). Twenty-four patients, 40-64 years old, received reduced-intensity conditioning (RIC) regimens. All RIC regimens contained fludarabine, combined with melphalan (n ¼ 19) or BU (n ¼ 5), and alemtuzumab or anti-thymocyte globulin (ATG) in the majority (n ¼ 19). Four patients (17%) in the RIC group had primary graft failure. Previous splenectomy reduced time to engraftment in the RIC group (13 versus 20 days; P ¼ 0.008). For MA and RIC groups, respectively, at 3 years, overall survival rates were 44 and 31% (P ¼ 0.67), progressionfree survival 44 and 24% (P ¼ 0.87), and actuarial relapse rates 15 and 46% (P ¼ 0.06). Non-relapse mortality at 3 years was 41% for the myeloablative and 32% for the RIC group. Acute GVHD occurred in 29 and 38% of patients in the myeloablative and RIC groups, respectively. Extensive chronic GVHD developed in 30 and 35% of evaluable patients, respectively.