We have conducted a direct comparison of the outcomes of reduced intensity and myeloablative conditioning in younger adults with hematological malignancies<50 yr. One hundred and five patients received transplants from human leukocyte antigen (HLA)-matched donors, via either reduced intensity (n=35) or myeloablative conditioning (n=70). The median ages of the reduced intensity and myeloablative groups were 36 and 33 yr (p=0.014). Neutrophil engraftment (i.e. time to absolute neutrophil count>0.5x10(9)/L) occurred more rapidly in the reduced intensity group (median: 10 d; range: 0-21 d) than in the myeloablative group (median: 18 d; range: 11-38 d; p<0.0001). The incidence of grades 2-4 acute graft-vs.-host disease were similar between the reduced intensity and myeloablative groups, at 17% vs. 24% respectively (p=0.40). The cumulative incidence of day 100 non-relapse mortality was 18% in the reduced intensity group, and 21% in the myeloablative group (p=0.88). The overall two-yr survival rates were 43% in the reduced intensity group, and 35% in the myeloablative group (p=0.72). In conclusion, reduced intensity transplantation yielded outcomes comparable with those of myeloablative transplantation in patients under 50 with hematological malignancies.