Factors influencing the outcome for 39 children with haematological malignancy who were subjected to a cord blood transplantation (CBT) from genotypically HLA-mismatched unrelated donors were analysed. This retrospective study included 21 children with acute lymphoblastic leukaemia, 15 with acute myelogenous leukaemia and one each with chronic myelogenous leukaemia, refractory anaemia with myelodysplastic syndrome (MDS) and juvenile myelomonocytic leukaemia (JMML). Those subjected to CBT during the first or second complete remission (CR) and MDS without blasts were assigned to the standard-risk (SR) group (n = 16). Patients in third or subsequent remission, relapse or partial remission with refractory leukaemia at the time of CBT were considered to be in advanced phase, and placed in the high-risk (HR) group (n = 11). JMML and the second CR after a relapse (n = 8), or bone marrow failure after a rejection (n = 3), following haematopoietic stem cell transplantation (HSCT) in the first CR were included in the high-risk group. Kaplan–Meier estimates for neutrophil and platelet recovery were 83·7 ± 12·2 at d 60 and 55·4 ± 16·6% at d 100 respectively. The incidence of grades II–VI acute graft-versus-host disease was 58·5 ± 16·8%. The Kaplan–Meier estimate for 3-year event-free survival (EFS) was 49·2 ± 16·6. From multivariate analysis, the most important factor influencing EFS was disease status at CBT: SR patients had a 3-year EFS of 75·0 ± 21·6%, compared with 29·6 ± 20·6% for those with HR disease (P = 0·013, RR 4·746, 95% CI 1·382–16·298). These data confirm that HLA-mismatched, unrelated CBT is a feasible procedure to cure a significant proportion of children with leukaemia, especially if conducted in a favourable phase of the disease.