Anemia is an indisputable finding in patients scheduled for coronary artery bypass graft (CABG) that can occur any time preoperatively. In presence of severe coronary artery disease, anemia can dramatically affect surgical outcomes. Therefore, we conducted this study to determine the effect of low preoperative hemoglobin (Hgb) on postoperative outcome in patients who underwent coronary artery bypass graft (CABG). In all, 4432 patients who had undergone isolated CABG at Tehran Heart Center over the 2-year period from March 2006 to February 2008 were studied. All medical records of the aforementioned patients were derived from our hospital surgery data bank. After adjustment for confounders, the association of different preoperative levels of Hgb with risk of cardiac, pulmonary, infectious, and ischemic complications, and also with prolonged ventilation and resource utilization, were assessed in a multivariable model. After adjustment for confounders that may affect mortality and morbidities, we found that cardiac, infectious, ischemic, and pulmonary complications, as well as postoperative mortality, were significantly higher in anemic patients compared to those with normal Hgb levels. In addition, total ventilation time, total intensive care unit hour stay (ICU), hospital length of stay (HLOS), and postsurgery length of stay (PLOS) were significantly longer in anemic patients. We concluded that isolated CABG patients with preoperative anemia have significantly higher mortality and morbidity, and use more health care resources. Preoperative anemia is an independent variable for increased resource utilization, morbidity, and mortality.