Objective: To analyze the anatomic characteristics of the left atrium and pulmonary veins in individuals undergoing ablation for atrial fibrillation and to identify possible anatomic factors related with recurrence. Material and methods: We retrospectively reviewed the CT angiography studies done to plan radiofrequency ablation for atrial fibrillation in 95 patients (57 men; mean age, 65 +/- 10 y). We reviewed the anatomy of the pulmonary veins and recorded the diameters of their ostia as well as the diameter and volume of the left atrium. We analyzed these parameters according to the type of arrhythmia and the response to treatment. Results: In 71 (74.7%) patients, the anatomy of the pulmonary veins was normal (i.e., two right pulmonary veins and two left pulmonary veins). Compared to patients with paroxysmal atrial fibrillation, patients with persistent atrial fibrillation had slightly larger diameter of the left pulmonary veins (left superior pulmonary vein 17.9 +/- 2.6 mm vs. 16.7 +/- 2.2 mm, p = 0.04; left inferior pulmonary vein 15.3 +/- 2 mm vs. 13.8 +/- 2.2 mm, p = 0.009) and larger left atrial volume (91.9 +/- 24.9 cm(3) vs. 70.7 +/- 20.3 mm(3), p = 0.001). After 22.1 +/- 12.1 months' mean follow-up, 41 patients had sinus rhythm. Compared to patients in whom the sinus rhythm was restored, patients with recurrence had greater left atrial volume (81.4 +/- 23.0 mm(3) vs. 71.1 +/- 23.2 mm(3), p = 0.03). No significant differences in pulmonary vein diameters or clinical parameters were observed between patients with recurrence and those without. Conclusion: The volume of the left atrium is greater in patients with persistent atrial fibrillation and in those who do not respond to ablation.