Hepatocellular carcinoma (HCC), cholangiocarcinoma (Chca) and benign bile ductule proliferations represent uncommon but important differential diagnoses in liver masses, especially if the patient has no known primary malignancy. The glucose transporter protein Glut-1 is commonly expressed in adenocarcinomas but its expression in HCC, Chca, and benign bile ductules has not been systematically investigated. Forty-two cases of Chca, 27 cases of benign bile ductule proliferations and 19 cases of HCC were stained with Glut-1. Cases were evaluated for a membranous staining pattern in tumor cells and the results compared. Twenty-one of 42 (50%) Chca stained with Glut-1 while no HCC or benign bile ductule proliferations did, neither did benign hepatocytes or portal triad structures. Glut-1 is a highly specific but insensitive stain for Chca. It may prove to be a helpful part of a diagnostic panel used to evaluate liver lesions.