Background: Subsequent development of atrial fibrillation (AF) is common after radiofrequency catheter ablation of typical atrial flutter (AFL); however, the risk factors of AF after successful AFL ablation have yet to be clearly established. This study investigates the prevalence of and risk factors for AF after successful AFL ablation. Methods: A total of 293 consecutive patients (236 men, mean age 56±14 years) without valvular heart disease who underwent radiofrequency catheter ablation of typical AFL were enrolled in the study. Results: AF was observed in 136 (46%) before ablation. During a follow-up of 40±37 months (1-199 months) 103 (35%) patients had AF after ablation including 37 (13%) newly diagnosed with AF. The patients with postablation AF had higher proportion of male sex (87% vs. 77%, p=0.003), had a larger LA diameter (43±6 vs. 41±6, p=0.03), and had AF before AFL ablation (65% vs. 36%, p<0.001) more frequently than those without postablation AF. In multivariate logistic regression analysis, male sex (OR 2.45, 95% CI 1.02-5.89, p=0.045) and AF before AFL ablation (OR 3.62, 95% CI 2.03-6.46, p<0.001) were significantly associated with the development of AF after AFL ablation. Conclusions: Patients with typical AFL undergoing successful ablation remain at an elevated risk for AF occurrence. Hypertrophic cardiomyopathy, AF before AFL ablation and male sex were independent risk factors of AF development after AFL ablation.