Background. Mortality attributable to bloodstream infection (BSI) is still controversial. We studied the impact of BSI on mortality after coronary artery bypass surgery, including the specific impact of different etiologic organisms. Methods. Our cohort consisted of 4515 patients who underwent coronary artery bypass procedures at a university hospital from 1996 through 2004. We used Society of Thoracic Surgery data supplemented with laboratory and infection control data. Mortality dates were identified using Society of Thoracic Surgery data and the Social Security Death Index. BSI within 90 days after surgery was defined by a positive blood culture result. Cox proportional hazards and propensity score models were used to analyze the association between BSI and mortality. Results. Patients with BSI had a 4.2-fold increased risk of death (95% confidence interval [CI], 3.0-5.9) 2-90 days after coronary artery bypass surgery, compared with uninfected patients. The risk of death was higher among patients with BSI due to gram-negative bacteria (hazard ratio [HR], 6.8; 95% CI, 3.9-12.0) and BSI due to Staphylococcus aureus (HR, 7.2; 95% CI, 3.3-15.7) and lowest among patients with BSI caused by gram-positive bacteria other than S. aureus (HR, 2.2; 95% CI, 1.1-4.6). The risk of death was highest among patients who developed BSI but had the lowest likelihood of infection (HR, 10.0; 95% CI, 3.5-28.8) and was lowest among patients who developed BSI but had the highest likelihood of infection (HR, 2.3; 95% CI, 1.2-4.6). Conclusions. BSIs due to gram-negative bacteria and BSIs due to S. aureus contributed significantly to mortality. Mortality attributable to BSI was highest among patients predicted to be least likely to develop infection and was lowest among severely ill patients who were most likely to develop infection. BSI appears to be an important contributor to death after coronary artery bypass surgery, particularly among the healthiest patients.