Abstract We analyzed the outcomes of 61 patients with hematologic malignancies who underwent double-unit cord blood transplantation (dCBT) after myeloablative conditioning performed as part of a prospective multicenter phase II study. The conditioning regimen for dCBT included total body irradiation, cyclophosphamide, and granulocyte colony-stimulating factor combined with cytosine arabinoside for myeloid malignancies and with total body irradiation and cyclophosphamide for lymphoid malignancies. The cumulative incidence of neutrophil engraftment after dCBT was 85% (95% confidence interval [CI], 73%-92%). All 51 of the patients who engrafted had complete chimerism derived from a single donor by day +60. Only the degree of HLA disparity in the host-versus-graft direction had an impact on unit dominance. The cumulative incidence of grade II-IV acute graft-versus-host disease was 25% (95% CI, 15%-37%), and that of chronic graft-versus-host disease was 32% (95% CI, 20%-44%). The 1-year cumulative incidence of relapse was 23% (95% CI, 13%-34%), and that of transplantation-related mortality was 28% (95% CI, 17%-39%). With a median follow-up of 41 months, event-free survival was 48% (90% CI, 37%-58%) at 1 year and 46% (90% CI, 35%-56%) at 3 years. Event-free survival at 3 years was 67% (95% CI, 46%-81%) for patients with standard risk and 29% (95% CI, 15%-45%) for those with advanced risk. This study suggests that dCBT after myeloablative conditioning is a promising alternative for adults and large children with hematologic malignancies who need stem cell transplantation but lack a suitable adult donor or an adequate single-unit cord blood graft.