Excellent late survival is expected after coronary artery bypass (CABG) in patients aged ≥80 years, but immediate postoperative mortality can be rather high. This study was planned to identify variables associated with very high operative risk in these fragile patients. This is a multicenter study including 2,246 patients aged ≥80 years who underwent isolated CABG at 68 Italian hospitals. The proportion of patients aged ≥80 years varied from 1.7 to 13.6 % (overall 5.6 %, p < 0.0001) in different institutions. The median logistic EuroSCORE varied from 6.2 to 31.7 % (overall median 11.3 %, p = <0.0001) in different institutions. Thirty-day mortality in patients aged ≥80 years correlated with that of patients aged <80 years (rho: 0.310, p = 0.027). The overall 30-day mortality rate was 6.5 %. Both logistic regression and CART showed that emergency procedure, low left ventricular ejection fraction, unstable hemodynamics, and use of nitrates infusion at arrival in the operating room were independent predictors of 30-day mortality. CART analysis showed that 30-day mortality among patients undergoing emergency CABG with unstable hemodynamic conditions was 32.60 % and it was 20.0 % in patients undergoing non-emergency operation with nitrates infusion at arrival in the operating room and left ventricular ejection fraction <30 %. The proportion and operative risk of patients aged ≥80 years and undergoing CABG significantly varied among institutions. Patients requiring emergency surgery, with unstable hemodynamic conditions, requiring nitrates infusion, and low ejection fraction have a prohibitive operative risk. This small proportion of patients may benefit from percutaneous coronary intervention in order to stabilize their preoperative conditions.