Background: The aims of this study are (1) to investigate the occurrence rate of postoperative complications in patients ≥ 80 years old after cardiac surgery and (2) to elucidate the impact of the most common postoperative complications on mortality.Methods: Between January 1998 and December 2007, 649 patients aged over 80 years received isolated first-time coronary artery bypass graft (CABG), isolated aortic valve replacement (AVR) or a combination of both in our institute. Prospectively entered patient data were analyzed with respect to major complications and outcome parameters.Results: Acute renal failure (55.0% vs. 7.5%, p = 0.0001), low cardiac out-put syndrome (43.1% vs. 8.8%, p = 0.0001), sepsis (52.0% vs. 10.3%, p = 0.0001), prolonged respiratory failure with tracheotomy (29.0% vs. 11.0%, p = 0.002), re-thoracotomy due to bleeding (26.9% vs. 10.6%, p = 0.0001), and postoperative laparotomy (30.8% vs. 11.5%, p = 0.033) had a significant impact on mortality. A multivariate analysis revealed that advanced age (OR 1.130, 95%CI; 1.017–1.256, p = 0.023), low output syndrome (OR 5.094, 95%CI; 1.1635–15.871, p = 0.005), renal failure (OR 8.128, 95%CI; 3.347–19.742, p = 0.0001) and sepsis (OR 4.975, 95%CI; 1.420–17.426, p = 0.012) as independent risk factors.Conclusions: The present study demonstrates that among major complications, low output syndrome, renal failure requiring renal replacement therapy and sepsis, dramatically impaired the postoperative course patients aged over 80 years undergoing CABG, AVR or combined CABG and AVR.