Recent studies have shown comparable survival outcomes for unrelated donor (URD) stem cell transplantation in chronic myelogenous leukemia compared to sibling donors. We compared outcomes for 105 patients aged 16 to 59 years undergoing URD transplants for acute myelogenous leukemia (AML) who were reported to the Australasian Bone Marrow Transplant Recipient Registry between 1992 and 2002, and a strictly selected matching set of 105 HLA-matched sibling donor (MSD) transplants. There was no significant difference between URD and MSD controls in the distributions of time from diagnosis to transplant, donor-recipient sex match, prior therapies, donor age, or performance status. The median follow-up of live URD patients was 4.4 years and for live MSD controls was 6.3 years. There were 18 good risk (complete remission [CR]1) and 87 poor risk (>CR1) recipients in both URD and sibling groups. Five-year disease-free survival (DFS) was not significantly different for good-risk URD and sibling donor recipients (62% versus 40%, P = .2), or poor-risk URD and sibling recipients (21% versus 25%, P = .2). In a stratified multivariate Cox regression model, the independent adverse risk factors for DFS were recipient cytomegalovirus positivity (P = .01) and the interaction of URD and earlier year of transplant (P = .006). Both neutrophil and platelet engraftment were significantly more rapid in the sibling group, but transplant-related mortality at 100 days was not significantly different. There was no difference in the cumulative incidence of acute graft-versus-host disease grade II or above at 100 days. Relapse occurred in 28% of good risk URD subjects and 16% of siblings (P = .3), and in poor risk subjects 39% and 29%, respectively (P = .2). Based on this data, URD allografts should be considered in AML patients without a matched sibling donor. This study provides a rationale for a larger prospective study of risk factors in allogeneic transplantation for AML and a guide on the subset of patients who may most benefit from an unrelated donor allograft in AML.