Veno-occlusive disease (VOD) of the liver occurs in 10% to 50% of patients after allogeneic stem cell transplantation, ranging from mild reversible disease to severe disease, with a mortality rate almost always close to 100%. Recently, promising results in the treatment of established VOD with defibrotide were reported. Therefore, defibrotide may be used as a prophylactic regimen for hepatic VOD in stem cell transplantation for hematologic malignancies. Fifty-two successive patients who underwent transplantation between October 1999 and June 2002 received defibrotide prophylaxis intravenously from day -7 to day +20 after transplantation in addition to heparin and were compared with historical controls who underwent transplantation successively between February 1997 and September 1999. In the defibrotide group, the maximum total bilirubin levels and the number of patients with serum levels exceeding 50 micromol/L were significantly lower than in the control group (5 of 52 versus 18 of 52, respectively; P =.004). None of the 52 patients developed VOD (Baltimore criteria), and no side effects occurred. These results were significantly different (P =.001) from controls (10/52 [19%] with VOD, 3 of whom died of severe VOD). In addition, day 100 event-free survival was significantly higher in the study group (P =.02), with a trend toward better day 100 overall survival (P =.07). These results suggest that defibrotide given in addition to heparin may be an efficient prophylaxis for VOD.