Umbilical cord blood (UCB) has increased access to hematopoietic cell transplantation (HCT) for patients without HLA-matched sibling donors (MSD). We compared outcomes of HCT using MSD (N=38) or UCB (N=60) among older patients (age ≥ 55 years) with AML or myelodysplastic syndromes (MDS). All patients received a reduced intensity regimen consisting of CY, fludarabine and 200 cGy TBI. Median age at HCT was 63 years for MSD and 61 years for UCB recipients. Among UCB recipients, 95% received two UCB units and 88% received 1-2 locus HLA-mismatched units to optimize cell dose. OS at 3-years was 37% for MSD and 31% for UCB recipients (P=0.21). On multivariate analysis, donor source (MSD vs UCB) did not impact risks of OS, leukemia-free survival and relapse or treatment-related mortality. UCB is feasible as an alternative donor source for reduced-intensity conditioning HCT among older patients with AML and MDS who do not have a suitable MSD.