BACKGROUND:: Atrial fibrillation (AF) is associated with increased morbidity in acute coronary syndrome patients, but impact on outcomes beyond 1 year is unclear. METHODS:: This was a post-hoc analysis from the long-tErm follow-uP of antithrombotic management patterns In acute CORonary syndrome patients (EPICOR) registry (NCT01171404), a prospective, observational study conducted in Europe and Latin America, which enrolled acute coronary syndrome survivors at discharge. Antithrombotic management patterns, mortality, a composite endpoint of death/new non-fatal myocardial infarction/stroke and bleeding events were assessed after 2 years of follow-up in patients with or without AF. RESULTS:: Of 10,568 patients enrolled, 397 (4.7%) had prior AF and 382 (3.6%) new-onset AF during index hospitalisation. Fewer patients with AF underwent percutaneous coronary intervention (52.1% vs. 66.6%; P<0.0001). At discharge, fewer AF patients received dual antiplatelet therapy (71.6% vs. 89.5%; P<0.0001); oral anticoagulant use was higher in AF patients but was still infrequent (35.0% vs. 2.5%; P<0.0001). Use of dual antiplatelet therapy and oral anticoagulants declined over follow-up with over 50% of all AF/no AF patients remaining on dual antiplatelet therapy (55.6% vs. 60.6%), and 23.3% (new-onset AF) to 42.1% (prior AF) on oral anticoagulants at 2 years. At 2 years, mortality, composite endpoint and bleeding rates were higher in AF patients (all P<0.0001) compared to patients without AF. On multivariable analysis, the risk of mortality or the composite endpoint was significant for prior AF ( P=0.003, P=0.001) but not new-onset AF ( P=0.88, P=0.92). CONCLUSIONS:: Acute coronary syndrome patients with AF represent a high-risk group with increased event rates during long-term follow-up. Prior AF is an independent predictor of mortality and/or ischaemic events at 2 years. Use of anticoagulants in AF after acute coronary syndrome is still suboptimal.