Early complications can be defined as those occurring within 100 days after transplant. Both epithelial and endothelial damage represent the pathogenetic basis for the onset of the most frequent complications. Clinical features related to endothelial damage depend on the involved district or on the grade and type of general distribution. Veno-occlusive disease (VOD) most often occurs within the first 20 days of haematopoietic SCT (HSCT) and is characterized by the obstruction of small intrahepatic venules and is caused by an initial injury of the sinusoid endothelial cells. The incidence in children ranges between 27 and 40%, and symptoms include hepatomegaly, portal hypertension and ascites. Early intervention with defibrotide (DF) proved to be effective for the treatment; however, overall mortality ranges between 20 and 50%. Thrombotic microangiopathy (TAM) incidence is 4-13%. It is often associated with the use of CYA or tacrolimus, and symptoms include haemolytic anaemia, thrombocytopenia and renal and/or central nervous system impairment. Treatment includes plasmapheresis and supportive care. The promising role of DF needs to be confirmed. The onset of engraftment syndrome may occur 1 or 2 days before the neutrophil count in peripheral blood increases. Clinical symptoms include fever not related to infection, respiratory involvement with pulmonary infiltrates or hypoxia and skin rash. Treatment consists of steroid administration for a few days. Haemorrhagic cystitis (HC) may occur early or later following transplant. Early-onset HC is related to mucosal damage caused by the catabolites of chemotherapy drugs, and late-onset HC is mostly caused by viral infections. The incidence ranges between 1 and 25%. Clinical symptoms include haematuria and dysuria without infections. Treatment includes hyperhydration and platelet support. In case of vescical clots, bladder irrigation is indicated. In advanced cases, hyperbaric oxygen administration or surgery may be useful. The use of cidofovir for BK virus-related HC seems encouraging, but further studies are needed to confirm its real efficacy.