This study retrospectively examined the impact of a single-nucleotide polymorphism (rs2275913, G197A) in the IL-17 gene of a total 510 recipients with hematologic malignancies and their unrelated donors on the clinical outcomes in HLA-matched myeloablative (discovery study) and nonmyeloablative (validation study) BMT through the Japan Marrow Donor Program (JMDP).