One hundred and ninety-one patients with acute leukaemia who received bone marrow from HLA-A, -B and -DR identical unrelated donors and were reported to EBMT and/or IMUST, were matched with 382 patients receiving autologous bone marrow for diagnosis, age, stage of disease and year of transplantation. Transplant-related mortality (TRM) was significantly higher in recipients of unrelated marrow compared to autograft recipients, 44 ± 4% (± 95% confidence interval) and 15 ± 3% at 2 years in the two groups, respectively (P < 10−4). In contrast, relapse probability was lower in recipients of unrelated marrow, being 32 ± 5% at 2 years compared to 55 ± 3% in recipients of autografts (P < 10−4). Two-year leukaemia-free survival (LFS) in patients with acute lymphoblastic leukaemia was 39 ± 5% and 32 ± 3% in the two groups, respectively. Among patients with acute myeloid leukaemia (AML), the corresponding figures were 36 ± 6% and 46 ± 5% in the two groups, respectively (P = NS). In AML in first remission (CR-1), the 2-year survival was 42 ± 10% in recipients of unrelated bone marrow, compared to 69 ± 8% in autograft recipients (P = 0.008). When all patients with acute leukaemia were included, the 2-year LFS was 38% in recipients of unrelated marrow, compared to 37% in autograft recipients (NS). In conclusion, this retrospective analysis supports the design of a prospective randomized study in patients with high-risk/advanced acute leukaemia who lack a suitable related bone marrow donor, to ascertain which of the two strategies, if any, should be favoured.