Since the first successful cord blood transplant was performed in 1988 there has been a gradual increase in the use of cord blood for hemopoietic stem cell transplantation. Worldwide, over 8,000 unrelated cord blood transplants have been performed with the majority being for children with hemopoietic malignancies. Transplantation for adults has increased but is limited by the low number of nucleated cells and CD34(+) cells within a single cord blood collection. Cord blood hemopoietic stem cells are more primitive than their adult counterparts and have high proliferative potential. Cord blood ex vivo expansion is designed to improve transplant outcomes by increasing the number of hemopoietic stem cells with long term repopulating potential and their differentiated progeny. However, despite a large amount of research activity during the last decade, this aim has not been realized. Herein we discuss the rationale for this approach; culture methods for ex vivo expansion, ways to assess the functional capacity of ex vivo generated hemopoietic stem cells and clinical outcomes following transplantation with ex vivo expanded cord blood.