Neonatal anaemias are frequent. Their mechanism is the same before and after birth, consisting of haemorrhage, haemolysis or abnormal red cell production. These anaemias are serious and may be life-threatening or disabling due to hypovolaemia and tissue hypoxaemia in the foetus or newborn, and to the risk of a possible hyperbilirubinaemia after birth. Blood transfusion in neonates must comply with very strict rules owing to the immunological characteristics of that period of life.