BACKGROUND Radiofrequency ablation is an effective treatment for typical atrial flutter (AFL) but long-term results may be hampered by atrial fibrillation (AF). OBJECTIVE To determine the incidence and predictors of AF during very long-term follow-up after radiofrequency ablation of typical AFL. METHODS From November 1998 to December 2000, patients who underwent successful radiofrequency ablation for cavotricuspid isthmus-dependent AFL in our centre were followed prospectively. RESULTS Of the 135 patients followed (mean age: 62+/-11 years), 69 (51%) had structural heart disease. Mean left ventricular ejection fraction was 52+/-11%. Patients were analysed according to preablation AF history: group 1 included patients with AFL (N=71); group 2 included patients with AFL and AF (N=64). During a median [interquartile range] follow-up of 7.8 [7.0-8.4] years, new-onset or recurrent AF was experienced by 99 (73%) patients: 44 (62%) in group 1 and 55 (86%) in group 2. Although most episodes occurred in the first 2 years postablation, AF prevalence increased continuously over time. Preablation AF history predicted AF occurrence (hazard ratio: 2.10, 95% confidence interval: 1.40-3.14; p=0.001), as did left atrial diameter (hazard ratio: 1.05 per 1 mm increase; 95% confidence interval: 1.02-1.08; p<0.001). AF evolved to become permanent in 24% of group 1 and 47% of group 2 patients (p=0.005). CONCLUSIONS During long-term follow-up, most patients will experience AF after ablation of typical AFL. Preablation AF history and left atrial enlargement predict postablation AF occurrence.