Umbilical cord blood (UCB) is potentially an attractive new source of hematopoietic stem cells. The extensive and ready availability of UCB offers important logistical advantages compared with traditional unrelated bone marrow. However, the initial concern about engraftment due to the low number of progenitor cells contained in a UCB unit, has limited the use of UCB, mainly for adult patients. In this review, we summarize the most important data available regarding the main aspects of unrelated-donor cord blood transplantation (UD-CBT) in adult patients. We will review the characteristics of UCB and their practical implications, the outcomes of and clinical results after UD-CBT used for hematological malignancies, and the current advances in UD-CBT designed to optimize this procedure. Current data confirm that UD-CBT is a reasonable alternative for those patients lacking a matched bone-marrow donor.