Human umbilical cord blood as an alternative source of hematopoietic stem cells for bone marrow reconstitution, has recently been demonstrated to yield successful HLA-matched placental blood grafts in children. It has been shown that cord blood contains sufficient progenitor cells to effect hematological reconstitution. Since then, more than 25 cord blood stem cells (CBSCs) transplants have been performed worldwide for the treatment of a variety of malignant and nonmalignant diseases. The majority of the grafts performed thus far have utilized CBSCs from HLA-identical siblings. However, much of the interest in this setting is devoted to the potential use of CBSCs for HLA-mismatched and unrelated transplants. Preliminary results suggest that allorecognition and graft-versus-host disease may be less intense in CBSCs transplants than in recipients of similarly compatible bone marrow. This review summarizes the results and potential future applications of cord blood transplantation.