In a systematic review and random-effects meta-analysis, we evaluated whether obesity is associated with postoperative atrial fibrillation (POAF) in patients undergoing cardiac operations. We selected 18 observational studies until December 2011 that excluded patients with preoperative AF (n = 36,147). Obese patients had a modest higher risk of POAF compared with nonobese (odds ratio, 1.12; 95% confidence interval, 1.04 to 1.21; p = 0.002). The association between obesity and POAF did not vary substantially by type of cardiac operation, study design, or year of publication. POAF was significantly associated with a higher risk of stroke, respiratory failure, and operative death.