The efficacy associated with peroral pancreatoscopy to diagnose and differentiate pancreatic diseases is herein reviewed and clarified, and problems with this modality are discussed. Three types of pancreatoscopes are presently available: (a) a thin fiberscope with a diameter of 3.3 or 4.5 mm, which has an angulation system and a forceps channel; (b) an ultrathin pancreatoscope with a diameter of 0.75 or 0.8 mm, which can be inserted via an ordinary endoscopic retrograde cholangiopancreatography (ERCP) cannula without endoscopic sphincterotomy; and (c) an ultrathin pancreatoscope combined with a catheter that has an outer diameter of 1.67 mm. Peroral pancreatoscopy facilitates the detection of small lesions of the duct in malignancy or chronic pancreatitis. In particular, it is quite useful in differentiating pancreatic cancer from chronic pancreatitis in cases with local stenosis or elevated lesions of the main pancreatic duct. Among patients with a mucus-producing tumor of the pancreas, pancreatoscopy is also very useful, especially in determining lesion extent. Despite some unresolved problems, we predict that pancreatoscopy will retain a limited or specific and definite role in diagnostic and therapeutic endoscopy for pancreatic diseases.