INTRODUCTION: Atrial fibrillation (AF) and flutter (AFL) are frequently associated. We assessed the frequency and identified the predictors of AF occurrence after AFL ablation. METHODS AND RESULTS: A total of 1,121 patients referred for AFL ablation were followed for a mean duration of 2.1 ± 2.7 years. Antiarrhythmic drugs were stopped after ablation in patients with no AF prior to ablation, or continued otherwise. A total of 356 patients (31.7%) had a history of AF prior to AFL ablation. Patients with AF prior to ablation were more likely to be females (OR = 1.35, CI = 1.00-1.83, P = 0.05). After ablation, 260 (23.2%) patients experienced AF. In the multivariable model, AF prior to ablation (OR = 1.90, CI = 1.42-2.54, P < 0.001) and female gender (OR = 1.77, CI = 1.29-2.42, P < 0.001) were associated with a higher risk of AF after ablation. In patients without prior AF, class I antiarrhythmics and amiodarone prior to AFL ablation were independently associated with higher risk of AF after ablation (OR = 2.11, CI = 1.15-3.88, P = 0.02 and OR = 1.60, CI = 1.08-2.36, P = 0.02, respectively). In patients who experienced AF after ablation, 201/260 (77.3%) had a CHA2DS2-VASc ≥1. Two patients with AF prior to ablation had a stroke during the follow-up whereas none of the patients without AF prior to ablation had a stroke. CONCLUSIONS: AF occurrence after AFL ablation is frequent (>20%), especially in patients with a history of AF, in female patients, and in patients treated with class I antiarrythmics/amiodarone prior to AFL. Since most patients who experience AF after AFL ablation have a CHA2DS2-VASc ≥1, the decision to stop anticoagulants after ablation should be considered on an individual basis.