Hypothesis: Outcome differences in octogenarians vs patients younger than 80 years undergoing coronary artery bypass grafting or valve surgery can be analyzed to isolate the effect of age alone on morbidity and mortality. Design: Eight-year hospitalization cohort study. Physicians, nurses, and perfusionists prospectively collected data on 225 variables. Setting: Community hospital. Patients: A consecutive sample of 7726 patients undergoing coronary artery bypass grafting or valve surgery between October 1, 1993, and February 28, 2001. Main Outcome Measures: There were 9 main outcomes of interest: mortality, length of hospital stay, gastrointestinal tract complications, neurologic complications, pulmonary complications, renal complications, return to intensive (fare unit, intraoperative complications, and reoperation to treat bleeding. We controlled for 16 potential confounding variables to isolate outcome differences according to age. Results: Of 7726 patients who fit the inclusion criteria, 522 were octogenarians. Compared with nonoctogenarians, octogenarians had a significantly higher New York Heart Association functional classification, higher incidence of hypertension, and underwent a greater number of coronary artery bypass grafting plus valve surgical procedures (P <.05). They also had significantly lower body surface area, fewer total number of grafts used, less history of tobacco use, and less abnormal left ventricular hypertrophy, and there were fewer nonwhite patients and fewer men. At multivariate analysis, octogenarians had a higher risk for death (relative risk [RR], 1.72; 95% confidence interval [CI], 1.52-1.83), longer hospital stay (RR, 1.03; 95% Cl, 1.01-1.04), more neurologic complications (RR, 1.51; 95% Cl, 1.26-1.67), and were more likely to undergo a reoperation to treat bleeding (RR, 1.49; 95% Cl, 1.09-1.72). Univariate analyses revealed no difference between octogenarians and non-octogenarians for diabetes mellitus, urgency of procedure, prior myocardial infarction, time since last myocardial infarction, cerebrovascular history, chronic obstructive pulmonary disease, or pump time. Conclusions: Age alone has been shown to influence outcomes after cardiac bypass or valve surgery. Octogenarians undergoing cardiac surgery have more comorbidities and higher mortality even after controlling for 16 potential confounding variables, compared with nonoctogenarians.