Human umbilical cord blood is a new source of hematopoietic stem cells. On the basis of prior laboratory investigations in an animal model and subsequent in vitro studies of human hematopoietic progenitors, umbilical cord blood was used to reconstitute hematopoiesis in a patient with Fanconi anemia in 1988. As a result of this first success, umbilical cord blood has been used in the treatment of 15 children with a variety of malignant and nonmalignant diseases, including acute and chronic leukemia, lymphoma, neuroblastoma, Fanconi anemia, aplastic anemia, Hunter syndrome, and congenital immunodeficiency. This review summarizes the brief history and potential future applications of cord blood stem cells (CBSCs) in transplantation.