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Umbilical cord blood (UCB) provides an alternative source of haematopoietic stem cells for patients with haematological diseases who lack HLA-matched, related or unrelated donors. Compared to other sources of stem cells, UCB is more readily available and makes it possible to extend transplants to a larger number of patients, even patients with rare haplotypes and HLA incompatibility. The choice of the cord blood unit (CBU) is mainly based on cell dose (both the number of nucleated cells and the number of CD34 positive cells) and HLA incompatibility. There is a clear association between these two parameters and the main outcomes of UCB transplantation (UCBT): neutrophil and platelet engraftment, transplant-related mortality (TRM), acute and chronic graft-versus-host disease (GVHD), relapse and survival. Compared to bone marrow transplantation, UCBT is associated with slower neutrophil and platelet engraftment, a lower incidence of acute and chronic GVHD, despite HLA disparities, and comparable TRM, relapse and survival rates, both in children and adults. Recently, the use of two CBU grafts (double transplant) has been investigated in order to improve cell dose and, consequently, allow adult patients to receive suitable grafts. Preliminary analysis shows that double UCBT is safe and associated with faster neutrophil recovery and higher engraftment rates than single UCBT. In addition, the use of reduced-intensity conditioning provides a valuable alternative with encouraging results, especially for elderly patients and those with comorbidities. [ABSTRACT FROM AUTHOR]