Unrelated umbilical cord blood (UCB) is an alternative stem cell source for paediatric patients lacking a matched related or unrelated marrow donor. We report the results of all paediatric unrelated UCB transplants performed in Australia and New Zealand over a 10-year period. A total of 135 patients were transplanted, 100 for malignant disease (74%) and 35 for non-malignant disorders. The majority (88%) of patients received an HLA-mismatched graft. The median infused total nucleated cell dose was 4.7 x 10(7)/kg and CD34+ count 1.9 x 10(5)/kg. Neutrophil engraftment occurred in 83% of patients by day 42 (median 23 days) and platelet engraftment in 55% by day 60 (median 56 days). Grades II-IV and III-IV acute GVHD occurred in 41 and 18% of patients, respectively. TRM and overall survival 1-year post transplant were 32 and 61%, respectively. A higher probability of neutrophil recovery (P=0.004) and faster time to recovery (median 18 days vs 26 days, P=0.008) were observed in recipients of a cord unit with a CD34 cell dose >or=1.7 x 10(5)/kg. Our results support selection of cord units with CD34 cell doses >or=1.7 x 10(5)/kg to promote faster engraftment, improve survival and lower TRM.