BACKGROUND Women have been found to have greater mortality from coronary artery bypass grafting than men. Uncertainty exists regarding the causes of the differences in outcomes between men and women after coronary artery bypass grafting. METHODS From a database of 2,569 patients having coronary bypass grafting we have determined factors that contribute to poorer outcomes in women compared with men. RESULTS Women were found to have greater mortality, postoperative bleeding, and postoperative pulmonary failure than men (p < 0.05). There was no significant difference between men and women in postoperative renal failure, postoperative infection, postoperative stroke, or intraaortic balloon pump (p = not significant). Patient factors other than sex accounted for all the significant predictors (stepwise logistic regression) of mortality, postoperative bleeding, postoperative renal failure, postoperative pulmonary failure, postoperative stroke, need for intraaortic balloon pump, and postoperative infection (p < 0.05). Poorer outcomes in women are associated with greater need for transfusion during operation. Diabetes is predictive of renal failure and stroke. CONCLUSIONS Mortality and morbidity is less in men despite their higher preoperative creatinine level, greater incidence of reoperation, lower ejection fraction, and more common atherosclerosis of the ascending aorta.