To evaluate the association between the Hematopoietic Cell Transplantation-Comorbidity Index (HCT-CI) and the recently developed age-adjusted HCT-CI (HCT-CI/age) and transplant outcomes in the setting of CD34-selected allogeneic HCT, we analyzed a homogeneous population of patients undergoing allogeneic HCT with CD34-selected grafts for acute myeloid leukemia and myelodysplastic syndrome (n= 346). Median HCT-CI and HCT-CI/age scores were 2 (percentile 25-75: 1-4) and 3 (percentile 25-75: 1-5), respectively. Higher HCT-CI and HCT-CI/age scores were associated with higher non-relapse mortality (NRM) and lower overall survival (OS). The HCT-CI distinguished two risk groups (0-2 vs. ≥3) whereas, with the HCT-CI/age, there was a progressive increase in NRM and decrease in OS with increasing scores in all 4 groups (0 vs. 1-2 vs. 3-4 vs. ≥ 5). Higher scores in both models were associated with lower chronic graft-versus-host disease relapse-free survival (CRFS), but not with higher relapse. Both models showed a promising predictive accuracy for NRM (c- = 0.616 for HCT-CI and c- = 0.647 for HCT-CI/age). In conclusion, the HCT-CI and HCT-CI/age predict transplant outcomes in CD34-selected allo-HCT, including NRM, OS and CRFS, and may be used to select appropriate patients for this approach.