Haploidentical hematopoietic cell transplantation (haplo-HCT) is being increasingly used in acute leukemia patients as an alternative transplant modality when matched sibling or matched unrelated donors are unavailable. As several potential haploidentical relative donors are typically available for a given patient, optimizing donor selection to improve clinical outcome is crucial. The impact of donor age and kinship on the outcome of acute leukemia patients is not clearly established in this setting. Using the multinational registry of the acute leukemia working party of the European society for blood and marrow transplantation we retrospective analyzed the clinical outcome of 1270 acute myeloid leukemia and acute lymphoblastic leukemia patients who underwent haplo-HCT between 2005 and 2015. Patients over the age of 40 were significantly affected by increasing donor age resulting in higher non-relapse mortality (NRM) [Hazard ratio (HR)=1.86, confidence interval (CI) 95%, 1.18-2.94; P = .007], inferior leukemia-free survival (LFS) (HR = 1.59, CI 95%, 1.13-2.24; P = .007), and overall survival (OS) (HR = 1.74, CI 95%, 1.22-2.47; P = .002) when donors were over the age of 40. Additionally, kinship was found to be prognostically significant as patients transplanted from children donors over the age of 35 experienced an increased rate of NRM (HR = 1.82, CI 95%, 1.13-2.9; P = .01), inferior LFS (HR = 1.5, CI 95%, 1.05-2.13; P = .03), and OS (HR = 1.5, CI 95%, 1.04-2.15; P = .03). For patients younger than 40 years, donor age and kinship were mostly not clinically impactful. Our data establish donor age and kinship as significant determinants of outcome following haplo-HCT for acute leukemia patients. © 2017 Wiley Periodicals, Inc.