Background-Left atrial (LA) remodeling is a factor in atrial fibrillation (AF) recurrence after pulmonary vein catheter ablation (CA), but right atrium (RA) remodeling has not been investigated for possible associations to AF recurrence. Methods and Results-Using 64-slice multidetector computed tomography, RA and LA volumes were measured 3-dimensionally before CA in 65 patients with initially proven idiopathic paroxysmal AF (mean age, 60 +/- 10 years, 81.5% men). The CA procedure was guided by CARTO Merge atrial electroanatomic mapping. Sixteen patients (24.6%) had AF recurrence within the 6-month period after the CA. The recurrence was associated with a large RA volume [odds ratio, 1.04; 95% confidence interval (CI), 1.02 to 1.07, P < 0.0001], a large LA volume with 1.04 [95% CI, 1.01 to 1.06, P=0.002], and low LA mean voltage with 1.03 [95% CI, 1.01 to 1.05, P=0.002]. After adjustment for potential confounding variables, RA and LA volumes remained predictive of AF recurrence. Large atrial volumes (mL) (RA >= 87 or LA >= 99) predicted AF recurrence (sensitivity of RA volume: 81.3% in 13 of 16 patients with AF recurrence; specificity: 75.5% in 37 of 49 patients without AF recurrence; sensitivity of LA volume: 81.3% in 13 of 16 patients with AF recurrence; specificity: 69.4% in 34 of 49 patients without AF recurrence), and the combined estimate of both atrial volumes was incremental and additive prognostic power (sensitivity: 75% in 12 of 16 patients with AF recurrence; specificity: 93.9% in 46 of 49 patients without AF recurrence). Conclusions-Both LA and RA remodeling are equally associated with post-CA AF recurrence. (Circ Cardiovasc Imaging. 2011;4:524-531.)