The number of cord blood transplants has been increasing very quickly with more than 250 cases reported to Eurocord Registry and more than 500 patients transplanted via the New York Cord Blood Bank. Cord blood transplants have been performed either with related or unrelated cord blood. Several cord blood banks established a group called Netcord whose goal is the standardization of the procedures, the organization of internal audits for accreditation and qualification, and the communication and exchange by internet of donor search on an international basis. More than 15,000 units of frozen cord blood are currently available and this number is increasing rapidly worldwide. Analysis of the clinical results has shown that related cord blood transplants give better results than unrelated cord blood transplants. Factors associated with better survival in related and unrelated cord blood transplants were lower age, diagnosis, with better results in inborn errors and in good risk children with acute leukemia. A larger number of nucleated cells in the transplant and the recipient being negative for CMV serology were also favourable risk factors for survival. Engraftment was improved with higher numbers of cells and HLA identity. Graft versus Host disease was reduced when compared to transplants of adult allogeneic bone marrow or peripheral blood progenitor cells. HLA disparities did not influence GVH; the only factor associated with increased GVH was positive CMV serology in the recipient. This study shows that cord blood is an alternative source of hematopoietic stem cells for allogeneic transplantation in children and in some adults. HLA disparity is not a limiting factor but the number of cells infused is important; currently the use of a number of nucleated cells inferior to 1 x 10(7)/kg is not recommended. Several questions remain including the criteria of choice of the donor, the indications in children and in adults, the comparison of cord blood transplants to other sources of hematopoietic stem cells and the role of growth factors and expansion for improving the speed of engraftment.