There have been rare comparative studies of hematopoietic stem cell transplantation from matched sibling donors (MSDs) and unrelated donors (URDs) with regard to peripheral blood stem cell transplantation (PBSCT). We performed a retrospective study of 104 consecutive acute myeloid leukemia (AML) patients who had received an allogeneic PBSCT from an MSD or a URD in order to compare transplant outcomes and posttransplant complications between the 2 groups of patients. The cumulative incidence of grade 2-4 acute graft-versus-host disease (aGVHD) at 100 days (22.6% with MSD vs. 35.3% with URD; p = 0.107) and that of chronic GVHD (cGVHD) at 2 years (72.9% with MSD vs. 56.1% with URD; p = 0.153) was not significantly different between the 2 groups. Multivariate analysis also indicated that a URD was not an independent predictor of grade 2-4 aGVHD or cGVHD. No statistically significant differences were observed in terms of relapse incidence (p = 0.371), nonrelapse mortality (p = 0.473), disease-free survival (p = 0.925) or overall survival (p = 0.534) at 2 years. URDs are comparable with MSDs as a donor type for PBSCT in AML patients if risk-stratified GVHD prophylaxis is adopted.