Forty-two consecutive pediatric patients with high-risk leukemia who received cord blood (CB) transplantation at the authors' institution from January 1996 and December 2007 were included in this study. Age ranged from 6 months to 18 years and body weight from 7 to 73 kg. Twenty-nine patients had ALL and 13 AML. Twenty-seven out of 42 patients were transplanted in advanced phase of disease (beyond 2nd CR). For 13 patients the CB transplantation was their second transplant. The median follow-up for survivors was 60 months (range, 6-120 months). The probability of myeloid engraftment was 95 ± 5% and the median time to neutrophil >500/μL was 20 days (range, 12-54). The median time to platelet engraftment was 60 days (range, 37-200). The probability of relapse was 33 ± 9%. The nonrelapse mortality at day +100 after transplantation was 30 ± 7%. The probability of disease-free survival was 34 ± 7%. The CD34⁺ cell dose had a significant impact on DFS (HR, 3.28; 95% CI: 1.49-7.23; p = .003). The results from a long-term follow-up study suggest that cord blood transplantation should be performed in the early phase of disease whenever possible. The cord blood unit for transplantation in pediatric patients with hematological malignancies should be chosen based on cell dose, especially a CD34⁺ cell dose.