The purpose of the study was to determine the difference in extrahepatic bile duct (EBD) size measured by magnetic resonance (MR) compared with those measured by ultrasound (US). Changes of EBD size related to aging were analyzed too. Size of EBD was measured in 76 randomly selected healthy individuals. Three radiologists blinded to the result of other study preformed measurements by US and three different T2 weighted MR sequences. Correlation and linear regression analysis of obtained data were performed. The mean diameter of EBD measured by US was 3.17 mm and by MR was 3.14 mm on thick slab rapid acquisition with relaxation enhancement (TSE), 3.26 mm on thin section single-shot TSE (HASTE) and 3.30 mm on coronal fully rewound gradient echo (True FISP). There was no statistical difference between US and different MR sequences (p < 0.05). A trend of increase of EBD with age (0.0155 mm per year, p = 0.0954) was observed. Size of EBD highly correlated for each MR sequence with US measurement validating use of MR as a reliable method for evaluation of EBD size. This conclusion is stressed by increase of EBD size with age demonstrated by all measuring methods.