At Odense University Hospital (OUH), 5-9% of all unselected cardiac surgical patients undergo reoperation due to excessive bleeding. The reoperated patients have an approximately three times greater mortality than non-reoperated. To reduce the rate of reoperations and mortality due to postoperative bleeding, we aim to identify risk factors that predict reoperation. A total of 1452 consecutive patients undergoing cardiac surgery using extracorporeal circulation (ECC) between November 2005 and December 2008 at OUH were analysed. Statistical tests were used to identify risk factors for reoperation. We performed a case-note review on propensity-matched patients to assess the outcome of reoperation for bleeding regarding morbidity and mortality. In total, 101 patients (7.0%) underwent surgical re-exploration due to excessive postoperative bleeding. Significant risk factors for reoperation for bleeding after cardiac surgery was low ejection fraction, high EuroSCORE, procedures other than isolated CABG, elongated time on ECC, low body mass index, diabetes mellitus and preoperatively elevated s-creatinine. Reoperated patients significantly had a greater increase in postoperative s-creatinine and higher mortality. Surviving reoperated patients significantly had a lower EuroSCORE and a shorter time on ECC compared with non-survivors. The average time to re-exploration was 155 min longer for non-survivors when compared with survivors.