We report here on three cases of mucinous ductal ectasia in which the diagnosis was suggested by abdominal computed tomography and finally established by duodenoscopy with pancreatoscopy. Duodenoscopic examination of the ampulla of Vater demonstrated a patulous papillary orifice and extrusion of viscid mucus. Pancreatoscopic examination was carried out in all three patients, and characteristic findings such as papillary or villous mucosal projections coated with whitish gelatinous mucus were noted. In patients with mucinous ductal ectasia in whom the radiographic findings are equivocal, pancreatoscopic examination may provide valuable information for the differential diagnosis of amorphous filling defects in the main pancreatic duct, and may provide information that helps to determine the extent of the pathology and the resection margin.