Various pretransplant patient and disease characteristics are associated with treatment-related mortality (TRM) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, TRM cannot yet be satisfactorily predicted. We prospectively investigated the aggregate impact of pretransplant clinical variables (period, donor/recipient age, gender, cytomegalovirus status, disease risk, stem cell source, and HLA matching), comorbidity index scores (Hematopoietic Cell Transplantation Comorbidity Index), and biological markers (telomere length, ferritin, and C-reactive protein) on TRM in single-center patients receiving a first allo-HSCT. From 2006 to 2012, all variables were available for 178 patients. In multivariate analysis, only mismatched unrelated donor (hazard ratio [HR], 2.79; 95% confidence interval [CI], 1.19-6.58; P = .019) and shorter age-adjusted recipient telomere length (HR, 2.17; 95% CI, 1.03-4.57; P = .041) were independently associated with TRM. Pre-allo-HSCT age-adjusted telomere length thus appears to be a useful new predictor of TRM in the setting of HSCT.