We audited 540 patients undergoing elective first-time coronary artery bypass grafts at 18 institutions. The purposes of the study were to describe the variability in transfusions among institutions and to determine factors that may account for variability. Mean homologous red blood cell use per patient was 2.9(±0.1) U (institutional range, 0.4 to 6.3 U). One hundred seventy-seven patients (32%) received plasma (institutional range, 0% to 97%), and 119 (22%) received platelets (institutional range, 0% to 80%). After controlling for patient and surgical practice variables, transfusion practice factors still accounted for variation in red blood cell transfusions. Variation in patients receiving plasma and platelet transfusions among institutions was determined in part by prophylactic transfusions. We conclude that blood component usage for coronary artery bypass grafts differs widely among institutions. The variability in use of these components is accounted for in part by unnecessary transfusions in otherwise routine, uncomplicated coronary artery bypass graft procedures.