Acute myeloid leukemia with monosomal karyotype (MK AML) carries a very poor prognosis, even after allogeneic stem cell transplantation (SCT). However, SCT remains the only curative option in this high-risk population. Because myeloablative conditioning regimen (MAC) is associated with less relapse, we hypothesized that more intensive conditioning regimen might be beneficial for MK AML patients. We reviewed 303 patients over age 45 diagnosed with either de novo or secondary MK AML. One hundred and five patients received a MAC and 198 a reduced-intensity conditioning (RIC). The median age at SCT was 57-year-old, significantly lower in the MAC (53-year-old) than in the RIC group (59-year-old). The median follow-up was 42 months (range, 3-156 months). The 3-year overall survival (OS), leukemia-free survival (LFS), and relapse rate (RR) were not significantly different between both groups with overall values of 34%, 29%, and 51%, respectively. On the contrary, the 3-year nonrelapse mortality (NRM) was significantly higher in MAC recipients (28%) compared with RIC patients (16%, P=0.004). The incidence of Grades II to IV acute graft-versus-host disease (GvHD) was significantly higher after a MAC (30.5%) than after a RIC (19.3%, P=0.02). That of chronic GvHD was comparable between both groups (35%) and did not impact on LFS. Interestingly, within our MK AML cohort, hypodiploidy was significantly associated with worse outcomes. Due to reduced toxicity and comparable OS, LFS, and RR, RIC appears as a good transplant option in the very high-risk population, including older patients, diagnosed with MK AML. Am. J. Hematol. 90:719-724, 2015. (c) 2015 Wiley Periodicals, Inc.