Introduction: Although umbilical cord blood (UCB) is an accepted alternative to bone marrow or peripheral blood (BM/PB) for transplantation, allele-matched BM/PB is generally regarded as the preferred graft source. Our aim is to compare leukemia-free survival (LFS) after transplantation of unrelated UCB and allele-matched BM/PB, and to provide guidelines for selection of an appropriate donor and graft source in children with acute leukemia. Patients and Methods: Outcomes of 22 children with acute leukemia and transplanted with single unit UCB were compared with outcomes of 34 BM/PB recipients. All transplantations were performed between May 2003 and June 2009. Recipients of UCB were transplanted with grafts that were HLA-matched (n=3) or HLA-mismatched for one (n=15) or two antigens (n=4). BM/PB recipients were transplanted with grafts that were HLA-matched (n=20) or mismatched (n=14). While allele-level typing for HLA-A, HLA-B, HLA-DRB1 and antigen-level typing for HLA-C was used for BM/PB transplantation, antigen level typing for HLA-A, HLA-B and HLA-DRB1 was used for UCB transplantation. Results: The median times to neutrophil and platelet recovery were 15 and 22 days after BM/PB transplantation, and 17 and 34 days after UCB transplantation, respectively. The 4-year probabilities of LFS were 58.0% after HLA-matched BM/PB transplants, 65.9% after HLA-mismatched BM/PB transplants, 66.7% after HLA-matched UCB transplants, 67.5% after one-mismatched UCB transplants with high cell dose (NC ＞ 3.0 x 10sup＞7/sup＞/kg), 40.0% after one-mismatched UCB transplants with low cell dose (NC 3.0 x 10sup＞7/sup＞/kg), and 33.3% after two-mismatched UCB transplants. The incidence of grade 3-4 acute graft-versus-host disease (GVHD) were 12.1% after BM/PB transplantation and 5.3% after UCB transplantation, respectively (i＞P/i＞=0.64). Rates of extensive chronic GVHD were 53.8% after BM/PB transplantation and 23.1% after UCB transplantation, respectively (i＞P/i＞=0.09). Transplant-related mortality rates were higher after UCB transplantation (21.7%) than BM/PB transplantation (2.9%) (i＞P/i＞=0.03). Relapse rates were similar after BM/PB transplantation (29.4%) and UCB transplantation (21.7%) (i＞P/i＞=0.56). Conclusion: These results support the use of HLA-matched or one-antigen HLA mismatched UCB in children with acute leukemia who need transplantation.