The impact of conditioning intensity on different disease risk index (DRI) groups has not been evaluated. We retrospectively analyzed acute myelogenous leukemia (AML)/myelodysplastic syndrome (MDS) hematopoietic cell transplantation (HCT) recipients in 2 groups based on DRI, to assess the impact of conditioning intensity on overall survival (OS), disease free survival (DFS), relapse, and nonrelapse mortality (NRM). A total of 380 patients with either high/very high (n = 148) or low/intermediate DRI (n = 232) myeloid malignancy (AML, n = 278; MDS, n = 102) were included in the analysis. Median follow-up for survivors was 35 months. Median age was 58years (range, 18 to 75). Patient and transplant-related characteristics were 41% reduced-intensity conditioning (RIC), 59% myeloablative conditioning (MAC), 13% bone marrow graft, 29% matched related donor, 49% matched unrelated donor, 22% haploidentical donor, and 52% HCT-specific comorbidity index ≥ 3. Among patients with high/very high DRI, there was no difference in OS, DFS, relapse, and NRM between RIC and MAC conditioning groups. For low/intermediate risk DRI recipients of MAC had better 3-year OS estimate (69% versus 57%, P = .001), DFS (65% versus 51%, P = .003), and lower relapse (3-year cumulative incidence, 17% versus 32%; P = .01) but similar NRM (19% versus 17%, P = .04) to RIC recipients. On multivariable analysis MAC was associated with better DFS (hazard ratio [HR], .58; 95% confidence interval [CI], .39-.88; P = .01), lower relapse (HR, .56; 95% CI, .32 to .97; P = .038), and similar NRM (HR, 1.11; 95% CI, .54 to 2.26; P = .781) compared with RIC in the low/intermediate DRI group. Intensity had no impact on HCT outcomes in the high/very high DRI group. MAC improves DFS and relapse compared with RIC among AML/MDS patients with low/intermediate DRI. The finding of no such benefit in high/very high DRI needs to be further explored in a larger cohort with a longer follow-up.