Approximately half of the patients presenting with acute coronary syndrome have multivessel disease. There has been conflicting data regarding the residual coronary artery disease (CAD) burden and its impact on mortality, especially in older people. Therefore, we aimed to assess all-cause mortality and residual CAD burden in older patients with acute coronary syndrome.Patients over 75 years of age who presented with acute coronary syndrome and underwent percutaneous coronary intervention were retrospectively included in the study. After the index procedure, residual The Synergy Between Percutaneous Coronary Intervention with Taxus and Cardiac Surgery (SYNTAX) scores were calculated and the patients were divided into two groups as residual SYNTAX > 8 and 8 (33.9% vs. 12.0% and 70.1% vs. 48.4% both p 8 (p 8, hazard ratio: 1.83 (1.30-2.56 95% confidence interval), p 8 had higher in-hospital and long-term all-cause mortality rates. Strategies aiming to reduce residual CAD burden by revascularization seem reasonable.