Preoperative aspirin therapy and reoperation for bleeding after coronary artery bypass surgery. We performed a case-control study to estimate the relative risk of reoperation for bleeding in coronary artery bypass graft patients who had taken aspirin within the 7 days preceding surgery. Comparison of 90 cases of reoperation with 180 matched control subjects gave an estimated odds ratio for reoperation of 1.82 (95% confidence interval, 1.23 to 3.32). Although their preoperative coagulation values were similar, cases used significantly more whole blood (cases, 9.5 +/- 5.2 units; control subjects, 3.0 +/- 2.0 units; median +/- interquartile range), packed red blood cells (cases, 2.1 +/- 4.0 units; control subjects, 0.9 +/- 2.0 units), and platelets (cases, 12.2 +/- 12.0 units; control subjects, 2.9 +/- 4.0 units) than control subjects. Cases had intensive care unit stays of 4.7 +/- 5.7 days (mean +/- SD) vs 2.1 +/- 1.9 days for control subjects and postoperative hospitalizations of 10.9 +/- 8.2 days vs 7.0 +/- 3.2 days for control subjects. We conclude that aspirin exposure within 7 days before coronary bypass surgery is associated with an increased rate of reoperation for bleeding and that reoperation is associated with large increases in transfusion requirements and intensive care unit and hospital stays. 