['In approximately two-thirds of patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT) no suitable related donor can be identified but an unrelated HLA-matched donor can be found through international donor registries. HSCT grafts from unrelated donors are commonly collected at distant sites. Therefore, graft storage and transportation becomes crucial in the HSCT process. We aimed to study the impact of graft quality on clinical outcome and identify factors affecting graft quality.', 'We investigated the influence of graft quality on the clinical outcome in 144 HSCT patients. Graft quality was assessed by determining the viability (7-aminoactinomycin D [7AAD]) on a frozen-thawed sample from the peripheral blood stem cell (PBSC) graft.', 'Patients receiving PBSCs with inferior quality (i.e., viability\u2009<\u200964% in the frozen-thawed sample) more frequently developed acute graft-versus-host disease (aGVHD) Grades I to IV than patients receiving grafts with better quality (p\u2009=\u20090.025). The transplant-related mortality (TRM) was higher in the group receiving grafts with lower viability (p\u2009=\u20090.03). The viability of the frozen-thawed samples was highly variable (median, 64%; range, 24%-96%). No correlation could be observed when comparing the viability in newly arrived PBSC grafts to frozen-thawed vials. Grafts with white blood cell (WBC) count of more than 300 × 10(9) /L had lower viability than those with lower WBC counts (p\u2009<\u20090.001).'] Does quality of the hematopoietic stem cell graft affect the clinical outcome of allogeneic stem cell transplantation?