Alloimmunization against platelet antigens may take place during pregnancy and following transfusion or transplantation. The resulting antibodies bind to the target platelet antigens and may lead to a rapid sequestration of incompatible platelets. The alloimmune thrombocytopenias are classified into neonatal alloimmune thrombocytopenia, post-transfusion purpura, passive alloimmune thrombocytopenia, transplantation-associated alloimmune thrombocytopenia, and platelet transfusion refractoriness. Neonatal alloimmune thrombocytopenia occurs in roughly one of 1,000 births and is the most important type in children. The management of affected infants during pregnancy is yet not established, and the most rapidly effective treatment after delivery is the transfusion of compatible platelets.