The prognostic role of previous coronary artery bypass (CABG) in elderly patients admitted to hospital for an acute coronary syndrome (ACS) is unclear. Therefore, the aim of this study was to compare the prognosis of patients aged ≥75 years admitted for an ACS with or without previous history of CABG. The primary outcome of the study was a composite of overall mortality, recurrent nonfatal myocardial infarction, nonfatal stroke, and rehospitalization for heart failure at 1-year follow-up. We included 2,253 ACS patients, aged 81 (78 to 85) years enrolled in 3 multicenter studies (the Italian Elderly ACS study, the LADIES ACS study, and the Elderly ACS 2 randomised trial) – 178 (7.9%) with previous CABG, 2,075 (92.1%) without. Patients with previous CABG had a higher burden of cardiovascular risk factors, lower ejection fraction, and higher creatinine values on admission. However, both at univariate analysis and after adjustment for the most relevant covariates (sex, age, previous myocardial infarction, type of ACS, left ventricular ejection fraction, and serum creatinine on admission), previous CABG did not show any statistically significant association with 1-year outcome (adjusted hazard ratio 0.85; 95% confidence interval 0.61 to 1.19; p = 0.353). In conclusion, our study suggests that elderly ACS patients with previous CABG have worse basal clinical characteristics. Nevertheless, in a broad cohort of patients mostly treated with percutaneous coronary intervention during the index event, previous CABG did not confer independent additional risk of major adverse cardiovascular events at 1-year follow-up.