Between 1996 and 1999, 172 patients (median age, 42 years) with hematologic malignancies were randomly assigned to receive either HLA-identical related bone marrow or G-CSF–mobilized peripheral blood mononuclear cells (G-PBMCs) after myeloablative conditioning. Early results showed that transplantation of G-PBMCs, compared with marrow, was associated with significantly superior 2-year disease-free survival (DFS) and overall survival. Ten-year follow-up showed a sustained DFS benefit associated with G-PBMCs (mortality or relapse hazard ratio, 0.64; 95% confidence interval, 0.4-1.0; P = .03), although the likelihood of overall survival was not significantly different between the 2 groups (mortality hazard ratio, 0.75; 95% confidence interval, 0.5-1.2; P = .20). The 10-year cumulative incidence of chronic GVHD and the duration of systemic immunosuppression were similar in the 2 groups. In summary, transplantation of HLA-identical related G-PBMCs, compared with marrow, was associated with superior short-term and long-term DFS, and there was no evidence that this benefit was outweighed by GVHD-related late mortality.