Background. Radical re-resection is offered to patients with non-metastatic, invasive, incidental gallbladder cancer. Data evaluating 18F-fluorodeoxyglucose positron emission tomography-computed tomography (18F-FDG PET-CT) in patients with incidental gallbladder cancer is sparse. Aim. To evaluate the efficacy of integrated 18F-FDG PET-CT in determining occult metastatic or residual local-regional disease in patients with incidental gallbladder cancer. Methods. Patients referred with incidental gallbladder cancer for radical re-resection were evaluated using multidetector computed tomography (MDCT) and PET-CT. Based on preoperative imaging, 24 out of 92 patients were found suitable for surgery. The two imaging modalities were evaluated with respect to residual and resectable disease. Results. In determining residual disease, MDCT had a sensitivity and positive predictive value (PPV) of 42.8%, each, while PET-CT had a sensitivity and PPV of 28.5 and 20%, respectively. In determining resectability, MDCT had a sensitivity, PPV, and accuracy of 100, 87.5, and 87.5%, respectively, as compared to PET-CT (sensitivity = 100%, PPV = 91.3%, accuracy = 91.6%). Conclusions. From our study, it appears that in patients with incidental gall bladder cancer without metastatic disease, PET-CT and MDCT seem to have roles complementing each other. PET-CT was able to detect occult metastatic or residual local-regional disease in some of these patients, and seems to be useful in the preoperative diagnostic algorithm of patients whose MDCT is normal or indicates locally advanced disease.