Elderly patients with acute syndrome are frailer due to the burden of comorbidity. Comorbidities that increase with age result in an increased risk of mortality in patients with acute coronary syndrome (ACS). Many scales have been developed to assess the burden of comorbidity, including the Charlson Comorbidity Index (CCI). The aim of our study is to show the effect of the CCI on 1-year mortality and poor clinical outcomes in elderly patients who underwent percutaneous coronary intervention due to ACS. This single-center retrospective study included 704 patients aged 75 years and older. The study population consisted of patients who were admitted to the hospital with ACS between April 2017 and September 2021 and underwent successful percutaneous intervention. The patients were divided into 3 groups according to their CCI scores as CCI 0 (n:156), 1 (n:266), and ≥2 (n:282). Stroke development was significantly higher in patients with CCI scores ≥ 2 compared to the other 2 groups (P= .005). Mortality rates were found to be 28.4%, 7.5%, and 2.6% in patients with CCI ≥ 2, CCI 1, and CCI 0, respectively. The mortality rate of the CCI ≥ 2 group was significantly higher than those of the other 2 groups (P< .001). The multivariate Cox proportional hazard regression model showed that CCI was an independent predictor for 1-year all-cause mortality (hazard ratio: 1.632; 95% confidence interval: 1.403–1.898;P< .001). CCI may contribute to treatment and follow-up management, as it indicates a poor prognosis in elderly patients who have undergone percutaneous coronary intervention.