To clarify the outcome of allogeneic hematopoietic cell transplantation (HCT) for leukemic transformation (LT) preceded by Philadelphia chromosome-negative (Ph-neg) myeloproliferative neoplasms (MPNs), we conducted a retrospective study using the national registry database of the Japan Society for Hematopoietic Cell Transplantation. From 2000 to 2013, 39 patients underwent their first allogeneic HCT with related bone marrow or peripheral blood stem cells (n = 8), unrelated bone marrow (n = 15), and unrelated umbilical cord blood (n = 16). The median patient age was 57 years. The underlying Ph-neg MPNs included 21 cases of essential thrombocythemia, 11 cases of primary myelofibrosis, and 7 cases of polycythemia vera. The median interval between the diagnosis of LT and transplantation was 134 days. Thirty-two cases (82%) were not in remission at the time of transplantation. The 2-year overall survival rate was 29.2% (95% confidence interval [Cl], 15.5% to 44.3%). The median follow-up of the surviving patients was 1989.5 days (range, 285 to 3270). The cumulative incidences of relapse and nonrelapse mortality at 2 years were 34.4% (95% CI, 19.6% to 49.8%) and 34.2% (95% CI, 19.6% to 49.4%), respectively. The study results suggested that allogeneic HCT provides long-term survival in approximately one-third of patients with LT preceded by Ph-neg MPNs. (C) 2016 American Society for Blood and Marrow Transplantation.