Adverse consequences of blood transfusion in children are not completely understood. Much remains to be learned about defining their mechanisms, learning how they can be avoided, and improving our understanding how to minimize the morbidity of their consequences. All types of transfusion reactions can occur in children. This article focuses on four adverse consequences that have particular relevance for pediatric populations: cytomegalovirus transmission, red blood cell alloimmunization, immune altering consequences of transfusion, and necrotizing enterocolitis. (C) 2016 Elsevier Inc. All rights reserved.