I.v. BU is frequently used in the conditioning regimen prior to allogeneic hematopoietic SCT (allo-HSCT); however, overall outcomes, incidence of hepatic sinusoidal obstructive syndrome (SOS) and its risk factors are not well known. With this aim, we performed a study on 257 AML adult recipients. Seattle Criteria were used for diagnosis and classification of SOS. The median age was 44 years. Donors were HLA-identical siblings in 60%, HLA-matched unrelated in 29% and HLA mismatched in 11%. Conditioning regimen was myeloablative in 84% (i.v. BU with CY was the most frequently used regimen) and it was reduced intensity in 16% (i.v. BU associated with fludarabine). Acute and chronic GVHD was observed in 28% and 44%, respectively. Two-year incidence of non-relapse mortality was 16 +/- 2% and 2-year leukemia-free survival for patients in CR1, CR2 and non remission at HSCT were 55 +/- 4%, 58 +/- 7%, and 20 +/- 5%, respectively. At 6 months, incidence of SOS was 7.8 +/- 2%; and it was severe in eight patients (3%). Factors associated with the occurrence of SOS were: HLA-mismatched donor HSCT (P = 0.002) and patients transplanted in non-remission (P = 0.002). In conclusion, outcomes of HSCT using i.v. BU are encouraging in this setting, SOS incidence is low and it is influenced by the type of donor and disease status at the time of transplant.