Large differences in patient and transplant backgrounds make it difficult to identify consistent prognostic factors of unrelated cord blood transplantation (UCBT) among different populations. Thus, we performed a collaborative study between Eurocord/ALWP-EBMT and JSHCT/JDCHCT. Adults with acute leukaemia who underwent a single UCBT were eligible. In total, 3764 and 1027 patients of the JSHCT/JDCHCT and Eurocord/ALWP-EBMT registries, respectively, were included. The median ages of the Japanese and European cohorts were 51 and 38 years, respectively. Three or more HLA mismatches were more frequently observed in the Japanese cohort. The median total nucleated cell (TNC) counts were 2.58 and 3.51 × 107/kg in the Japanese and European cohorts, respectively. Anti-thymocyte globulin was used in only 2% of the Japanese cohort compared with 65% of the European cohort. The 3-year overall survival (OS) was 41% in JSHCT/JDCHCT and 33% in Eurocord/ALWP-EBMT. In the multivariate analysis, TNC dose and HLA matching had no significant effect on OS in either cohort, whereas year of transplantation, age, and refined disease risk index affected OS in both cohorts. Despite considerable differences in characteristics between the Japanese and European cohorts, we observed similar prognostic factors affecting UCBT outcomes in adult patients with acute leukaemia in both registries.