Gemtuzumab ozogamicin (GO) may increase the risk of sinusoidal obstruction syndrome (SOS) when used prior to allogeneic stem cell transplantation (HSCT). We assessed SOS incidence and outcomes after HSCT of 146 adults, with a median age of 50 years, previously receiving GO. SOS prophylaxis was used in 69 patients (heparin n=57, ursodeoxycholic acid n=8, defibrotide n=4). Cumulative incidence (CI) of SOS was 8% (n=11), with death in 3 patients. Median interval between last GO dose and HSCT was 130 days. Overall survival (OS) and SOS incidence did not differ for patients receiving GO ≤3.5 months before HSCT and the others. CI of acute and chronic GVHD was 31% and 25%, respectively. Probability of OS and leukemia-free survival (LFS) at 5 years was 40% and 37%, respectively. Relapse incidence and non-relapse mortality were 42% and 21%, respectively. In multivariate analysis, active disease at HSCT was associated with relapse and worse LFS and OS (P<0.03). Liver abnormalities before HSCT correlated with worse OS (P<0.03). Use of low-dose GO prior to HSCT is associated with an acceptable SOS incidence. Prospective studies investigating the role and the utility of SOS prophylaxis are warranted.