BACKGROUND: Antithrombotic therapy for acute myocardial infarction (MI) with atrial fibrillation (AF) among higher risk older patients treated with percutaneous coronary intervention (PCI) remains unclear. OBJECTIVES: This study sought to determine appropriate antithrombotic therapy for acute MI patients with AF treated with PCI. METHODS: We examined 4,959 patients ≥65 years of age with acute MI and AF who underwent coronary stenting (Acute Coronary Treatment and Intervention Outcomes Network Registry-Get With the Guidelines). The primary effectiveness outcome was 2-year major adverse cardiac events (MACE) comprising death, readmission for MI, or stroke; the primary safety outcome was bleeding readmission. Outcomes with dual antiplatelet therapy (DAPT) or triple therapy (DAPT plus warfarin) were compared using Cox proportional hazard modeling with inverse probability-weighted propensity adjustment. RESULTS: Among 4,959 patients, 27.6% (n = 1,370) were discharged on triple therapy. Relative to DAPT, patients on triple therapy had a similar risk of MACE (adjusted hazard ratio [HR]: 0.99 [95% confidence interval (CI): 0.86 to 1.16]) but significantly greater risk of bleeding requiring hospitalization (adjusted HR: 1.61 [95% CI: 1.31 to 1.97]) and greater risk of intracranial hemorrhage (adjusted HR: 2.04 [95% CI: 1.25 to 3.34]). Of 1,591 Medicare Part D patients, 90-day post-discharge warfarin persistence among patients discharged on warfarin was 93.2% (n = 412). Results of 90-day landmark analyses comparing triple therapy versus DAPT in patients persistently on warfarin versus those not discharged on warfarin who had not filled a warfarin prescription were similar to our primary findings. CONCLUSIONS: Approximately 1 in 4 older AF patients undergoing PCI for MI were discharged on triple therapy. Those receiving triple therapy versus DAPT had higher rates of major bleeding without a measurable difference in composite MI, death, or stroke.