BACKGROUND Diabetes mellitus (DM), chronic kidney disease (CKD), and advanced age are associated with poor outcomes in patients with acute coronary syndrome (ACS). This real-world study utilized data from the Taiwan Chang Gung Research Database (CGRD) to compare outcomes in ACS patients with DM, CKD, and the elderly. MATERIAL AND METHODS The study enrolled 28,613 ACS patients diagnosed based on CGRD medical records between January 2005 and December 2019. Baseline characteristics and clinical outcomes were compared among groups based on patient characteristics. RESULTS Within the ACS cohort, 42.1% had DM, 48.2% had CKD, and 33.6% were elderly. Among them, 10.7% (3,070) were elderly patients with both DM and CKD. Elderly patients with DM and CKD had significantly higher risks of gastrointestinal bleeding (hazard ratio=11.32), cardiovascular events (HR=7.29), and all-cause mortality (HR=8.59). Patients with three or at least two of these risk factors had a 2.20-2.99-fold increased risk of recurrent ACS during the three-year follow-up period. CONCLUSIONS Patients with the combination of DM, CKD, and advanced age (elderly) experienced an 11.32-fold increased risk of gastrointestinal bleeding, 7.29-fold increased risk of cardiovascular events, and 8.59-fold increased risk of all-cause mortality compared to those without these risk factors. Furthermore, patients with two or more of these risk factors had a 2- to 3-fold increased risk of recurrent ACS. These findings emphasize the importance of managing multiple risk factors in ACS patients to improve outcomes.