['To examine the mortality risk of blood transfusions when donor information, postdonation treatment, and a wide selection of risk factors are taken into account.', 'A retrospective study was performed on 9907 patients who underwent coronary artery bypass grafting and/or aortic valve replacement. Several transfusion-related risk factors, including age of blood products, sex of donor, ABO group, Rh group, posttransfusion treatment, and sex matching, were included in the analysis. A wide selection of preoperative comorbidities were included as well. A Cox proportional hazards analysis was performed to determine significant risk factors. Patients were followed for a period of up to 12\xa0years posttransfusion.', 'We found an excess mortality for transfusions of sex-mismatched red blood cells (RBCs) per unit transfused (hazard ratio [HR], 1.083; 95% confidence interval [CI] 1.028-1.140; P\xa0=\xa0.003). In addition, we found a significant risk during the first year for transfusing 1 to 2 units of non-leukocyte-depleted RBCs (HR, 1.426; 95% CI, 1.004-2.024; P\xa0=\xa0.047). Transfusion of 1 to 2 units of leukocyte-depleted RBCs was not associated with increased risk (HR, 0.981; 95% CI, 0.866-1.110; P\xa0=\xa0not significant). The age of blood products was not associated with increased mortality.'] Does transfusion of sex-mismatched and non-leukocyte-depleted red blood cells in cardiac surgery increase mortality?