Veno-occlusive disease (VOD) of the liver remains one of the most feared complications associated with high-dose chemotherapy and hematopoietic stem cell transplantation (SCT). As a clinical syndrome characterized by fluid retention, hyperbilirubinemia, and painful hepatomegaly, VOD incidence varies widely, but it is universally recognized that severe cases of VOD have an extremely poor prognosis, with mortality at day 100 after SCT in excess of 80%. Systemic anticoagulant and thrombolytic therapies have been tested extensively in this disease, but are largely ineffective and are associated with significant bleeding complications. In recent years, defibrotide (DF; a polydisperse oligonucleotide derived from porcine intestinal mucosa with antithrombotic and protective properties on the microvasculature but minimal hemorrhagic risk) has emerged as a promising therapy for VOD. In large, multicenter, international phase I/II trials targeting patients with severe VOD, DF has been associated with complete response rates between 36 and 60%, survival past transplant day 100 in the range of 32 to 50%, and few significant attributable side effects. On the basis of these encouraging results, a pivotal, prospective, multinational, phase III trial of DF is underway in patients with severe VOD, and should provide validation of this agent as a therapy for established disease with a high risk of mortality. This article reviews our current understanding of hepatic VOD after SCT and provides a summary of the data to date on the use of DF as both therapy and prophylaxis for this disease.