Outcomes for adolescents and young adults (AYAs) with leukemia differ from other age groups and are still under-represented in clinical research. The aim of this study was to analyze outcomes of umbilical cord blood transplant (UCBT) in AYAs with acute leukemia reported to Eurocord/European Society for Blood and Marrow Transplantation. Patients (N = 504) had acute lymphoblastic (59%) or myeloid leukemia (41%), were aged 15 to 25 years, and received UCBT after myeloablative conditioning regimens between 2004 and 2016. The primary endpoint was 3-year overall survival (OS). Median follow-up was 3.9 years. Transplant was single in 58% and double UCBT in 42%. Three-year OS was 45% and leukemia free survival (LFS) was 41%. Cumulative incidence functions (CIFs) of nonrelapse mortality (NRM) and relapse were 31% and 28%, respectively. CIF of acute graft-versus-host disease (GVHD) grades II to IV at day 100 was 28%. Three-year CIF of chronic GVHD was 25%. In adjusted analysis, better disease status at UCBT (hazard ratio [HR], 2.74; P < .001) and more recent UCBT (HR, 1.43; P = .01) were associated with increased OS, and a similar effect of these factors was observed on LFS. Contrastingly, the use of antithymocyte globulin had a negative effect in LFS. The risk of acute GVHD grades II to IV increased with the use of double UCBT (HR, 1.65; P  = .02) and decreased with more recent transplant period (HR, .65; P = .02) and antithymocyte globulin use (HR, .55; P  = .01). Outcomes of AYA UCBT improved in more recent years, becoming comparable with pediatric results. Demonstrating the feasibility of UCBT in AYAs facilitates stem cell source selection and provides the basis for future prospective studies.