BACKGROUND: The prognostic benefit of complete revascularization in elderly patients (aged over 75 years) with multi-vessel disease and acute coronary syndrome (ACS) is currently unclear. This study aimed to determine the long-term prognostic impact of complete revascularization in this population. METHODS: We conducted this study using data obtained from the BleeMACS (Bleeding complications in a Multicenter registry of patients discharged after an Acute Coronary Syndrome) registry, which was carried out from 2003 to 2014. The objective was to categorize older patients diagnosed with ACS into two groups: those who underwent complete revascularization and those who did not. Propensity score matching and the Kaplan-Meier analysis were employed to examine differences in one-year clinical outcomes. The primary endpoint was major adverse cardiovascular event (MACE), which encompassed a combination of all-cause mortality and myocardial infarction. RESULTS: Out of 1263 patients evaluated, 445 patients (35.2%) received complete revascularization. Patients who underwent complete revascularization had a higher prevalence of hypertension and prior percutaneous coronary intervention compared to those who did not. During the one-year follow-up period, complete revascularization was associated with a significantly decreased risk of MACE [13.7% vs. 20.5%, hazard ratio (HR) = 0.63, 95% CI: 0.45-0.88, P = 0.007] and a lower risk of myocardial infarction (5.9% vs. 9.9%, HR = 0.55, 95% CI: 0.33-0.92, P = 0.02). However, it was not linked to a lower risk of all-cause death (9.5% vs. 13.5%, HR = 0.68, 95% CI: 0.45-1.02, P = 0.06). Similar results were observed in the subgroup analysis. CONCLUSIONS Long-term clinical improvements were observed in ACS patients aged over 75 years with multi-vessel disease who achieved complete revascularization. Therefore, adhering to guidelines for complete revascularization should be recommended for elderly patients.