Background: Atrial fibrillation is a frequent cause of morbidity following coronary artery bypass grafting (CABG). SYNTAX score II (SSII) is associated with outcomes in patients undergoing coronary revascularization. We investigated the relationship between SSII and postoperative atrial fibrillation (POAF) in patients undergoing CABG. Methods: Records of 461 consecutive patients who underwent elective isolated CABG were retrospectively reviewed. Characteristics of patients with and without POAF were compared. Results: POAF developed in 51 (11.1%) patients. Patients with POAF were older (61.8 ± 7.8 versus 58.4±7.7; P = .003). Chronic obstructive pulmonary disease (COPD) and history of coronary artery disease (CAD) were more frequent in patients with POAF whereas the frequency of hypertension (HT), diabetes mellitus (DM), and smoking did not differ. CRP was significantly higher in patients with POAF. Left atrial diameter (LAD), EuroSCORE II, SSI and SSII were greater in patients with POAF (P < .001 for all). Age, history of CAD, LAD, SSI, and SSII were independent predictors of POAF in multivariate regression analysis. In ROC analysis, SSII was more accurate than SSI for predicting POAF, albeit statistically insignificant [difference between AUC: 0.0483, 95% CI (-0.0411) - (0.138); z statistic:1.059, P = .29)]. In-hospital MACE (3.2% versus 9.8%, P = .038) and one-year mortality (4.6% versus 13.5%, P = .008) of patients with POAF were significantly higher. Conclusion: POAF occurred in more than one-tenth of patients undergoing CABG, and it is associated with in-hospital MACE and one-year mortality. Age, history of CAD, LAD, SSI, and SSII are independent predictors of POAF. SSII seems to be more accurate than SSI for predicting POAF.