Sinusoidal obstruction syndrome (SOS), also known as hepatic veno-occlusive disease (VOD), is a well-known complication of allogeneic hematopoietic stem cell transplantation (HSCT) associated with a mortality rate of up to 85%. Defibrotide has shown efficacy in treatment of SOS/VOD. Moreover, evidence exists supporting the efficacy of defibrotide as SOS/VOD prophylaxis. We have previously reported our single center experience on 52 HSCT recipients receiving defibrotide as SOS/VOD prophylaxis, which has shown that the patients did not develop any SOS/VOD under this prophylaxis. The aim of the present study was to see if we can confirm the previous results, mainly on the decrease incidence of SOS/VOD, as well as improve event-free survival (EFS) on a larger study population. We extended our previous study in a single-center retrospective analysis to include 237 consecutive patients (248 transplantations) who underwent transplantation between 1999 and 2009 for hematological diseases and receiving intravenous defibrotide as prophylaxis. This cohort was compared to 241 patients (248 transplantations) treated before 1999 or after 2009 when defibrotide prophylaxis was not routinely used in our center. Median follow-up for the study group was 10 (range 2-16) years and for the control group 2.7 (range 1-18) years. None of the 237 patients in the defibrotide group developed SOS/VOD. The cumulative incidence (CI) of SOS/VOD was 0% in the defibrotide group as compared to 4.8% (95% confidence interval [CI], 2.6-8%; P= .00046) in the control group. There was also a better 1-year EFS with 38% (95% CI, 32%-44%) in the defibrotide group versus 28% (95% CI, 22%-34%) (P= .00969) and decreased cumulative incidence of acute graft-versus-host disease (GvHD) in the defibrotide group 31% (95% CI, 25%-37%) versus 42% (95% CI, 36%-48%) (P= .026). The 1-year overall survival, relapse incidence, and non-relapse mortality were not statistically different. Multivariable analysis, performed taking into account clinical factors known to influence the risk of SOS/VOD, confirmed the favorable impact of defibrotide on SOS/VOD (HR 1.38e-08 [95% CI, 3.28e-09-5.80e-08]; P< .00001). Conversely, multivariable analysis failed to confirm the impact of defibrotide on 1-year EFS or acute GvHD. This large retrospective study on SOS/VOD-prophylaxis with defibrotide suggests that this approach may be of benefit. These results need to be confirmed in a prospective randomized trial.