Sinusoidal obstruction syndrome (SOS), previously known as veno-occlusive disease, is characterized by concentric and non-thrombotic obstruction of the sinusoid and central vein lumen with no identified primitive or thrombotic hepatic vein lesions. The initial lesion is a result of endothelial denudation, corresponding to the migration of damaged sinusoidal cells to the central veins of the hepatic lobules, leading to sinusoidal and veno-occlusive congestive obstruction. SOS may be associated with other lesions such as centrilobular perisinusoidal fibrosis, peliosis, or nodular regenerative hyperplasia. The first cases of SOS were documented in 1920 in South Africa, after ingestion of food sources contaminated by pyrrolizidine alkaloids. SOS is a well-known complication of hematopoietic stem cell transplantation (HSCT). Numerous toxins and drugs have been associated with SOS, mainly chemotherapies and immunosuppressive therapies, as well as total body or liver irradiation and ABO mismatch platelet transfusion. The pathogenesis of this entity remains unknown.