Defibrotide for use in prophylaxis and/or treatment of Graft versus Host Disease (GVHD) in humans is disclosed, preferably in hematopoietic stem cell transplantation (HSCT), more preferably allogeneic hematopoietic stem cell transplantation. Graft versus Host Disease of the invention (GVHD) can be acute aGVHD and/or chronic cGVHD, preferably acute.