Our goal was to evaluate fluorodeoxyglucose (FDG) positron emission tomography (PET) in staging patients with biliary tract cancers. Fifty consecutive patients who underwent FDG-PET for suspected cholangiocarcinoma (n=36) or gallbladder carcinoma (n=14) were reviewed. Patients with cholangiocarcinoma were divided into two groups: group 1 had nodular type (mass=1 cm) (n=22) and group 2 had infiltrating type (n=14) cholangiocarcinoma. Thirty-one of 36 patients evaluated for cholangiocarcinoma had cholangiocarcinoma and five did not. Sensitivity was 85% for nodular morphology but only 18% for infiltrating morphology. Sensitivity for metastases was 65% but false negative for carcinomatosis in three of three patients. One false positive result occurred in a patient with primary sclerosing cholangitis who had acute cholangitis. Seven (58%) of 12 patients had FDG uptake along the tract of a biliary stent. FDG-PET led to a change in surgical management in 30% (11 of 36) of patients evaluated for cholangiocarcinoma because of detection of unsuspected metastases. Eleven of 14 patients with gallbladder carcinoma were newly diagnosed by cholecystectomy or another type of exploratory procedure, whereas three patients were undergoing follow-up. Nine had residual gallbladder carcinoma at the time of PET. Sensitivity for gallbladder carcinoma was 78%. Sensitivity for extrahepatic metastases was 50% in eight patients; six of them had carcinomatosis. These data suggest that PET is accurate in predicting the presence of nodular cholangiocarcinoma (mass>1cm) but was not helpful for the infiltrating type. PET was also helpful for detecting residual gallbladder carcinoma following cholecystectomy, but was not helpful in patients with carcinomatosis. Although FDG-PET led to a change in management in 30% of patients with cholangiocarcinoma, it must be interpreted with caution in patients with primary sclerosing cholangitis and with stents in place, as well as in those with known granulomatous disease.