Incident atrial fibrillation (AF) is common after cavotricuspid isthmus (CTI) dependent atrial flutter (AFL) ablation. Risk factors for development of AF post ablation are not well understood. To identify patients undergoing CTI ablation for AFL most likely to develop AF. We identified 114 patients without history of AF who underwent CTI AFL ablation. We evaluated baseline characteristics, electrophysiology study (EPS) data and echocardiographic data for incidence of AF within 3 years. Incident AF was identified in 46 patients (40%) during 600 + 405 days follow-up. Left atrial volume index (LAVI) was significantly greater in patients who developed AF compared to those that did not (37  12.2 ml/m2 vs 30  13.4 ml/m2, p=.004). EPS data was similar between groups. Area under the receiver operator characteristic curve based on the LAVI for prediction of AF was 0.7 (p = 0.004). Kaplan-Meier estimated incidence of AF was significantly greater in patients with LAVI ≥ 30 ml/m2 than LAVI < 30 ml/m2 (66% vs 27%, p=0.004). Risk of incident AF in patients with LAVI > 40 mL/m2 was similar to that of LAVI 30-40 ml/m2 (67% vs 63%, respectively, p=0.97). In multivariate analysis LAVI remained the sole independent predictor of incidence AF after CTI AFL ablation. LAVI ≥ 30 ml/m2 is associated with significantly increased risk of incident AF following CTI ablation for typical AFL. The utility of elevated LAVI for identifying patients that may benefit from intensified arrhythmia monitoring, or prophylactic AF ablation requires further evaluation.