AIM: To investigate if transnasal endoscopic retrograde cholangiopancreatography (n-ERCP) using an ultrathin forward-viewing scope may overcome the disadvantages of conventional oral ERCP (o-ERCP) related to the large- caliber side-viewing duodenoscope. METHODS: The study involved 50 patients in whom 25 cases each were assigned to the o-ERCP and n-ERCP groups. We compared the requirements of esophagogastroduodenoscopy (EGD) prior to ERCP, rates and times required for successful cannulation into the pancreatobiliary ducts, incidence of post-procedure hyperamylasemia, cardiovascular parameters during the procedure, the dose of a sedative drug, and successful rates of endoscopic naso-biliary drainage (ENBD). RESULTS: Screening gastrointestinal observations were easily performed by the forward-viewing scope and thus no prior EGD was required in the n-ERCP group. There was no significant difference in the rates or times for cannulation, or incidence of hyperamylasemia between the groups. However, the cannulation was relatively difficult in n-ERCP when the scope appeared U-shape under fluoroscopy. Increments of blood pressure and the amount of a sedative drug were significantly lower in the n-ERCP group. ENBD was successfully performed succeeding to the n-ERCP in which mouth-to-nose transfer of the drainage tube was not required. CONCLUSION: n-ERCP is likely a well-tolerable methodwith less cardiovascular stress and no need of prior EGD or mouth-to-nose transfer of the ENBD tube. However, a deliberate application is needed since its performance is difficult in some cases and is not feasible for some endoscopic treatments such as stenting. A investigator: To investigate if transnasal endoscopic retrograde cholangiopancreatography (n-ERCP) using an ultrathin forward-viewing scope may overcome the disadvantages of conventional oral ERCP (o-ERCP) related to the large- caliber side-viewing duodenoscope. METHODS: The study involved 50 patients in whom 25 were each assigned to the o-ERCP and n-ERCP groups. We compared the requirements of esophagogastroduodenoscopy (EGD) prior to ERCP, rates and times required for successful cannulation into the pancreatobiliary ducts, incidence of post-procedure hyperamylasemia, cardiovascular parameters during the procedure, the dose of a sedative drug, and successful rates of endoscopic naso-biliary drainage (ENBD). RESULTS: Screening gastrointestinal observations were easily performed by the forward-viewing scope and thus no prior EGD was required in the n-ERCP group. There was no significant difference in the rates or times for cannulation, or incidence of hyperamylasemia between the groups. Ho wever, the cannulation was relatively difficult in n-ERCP when the scope appeared U-shape under fluoroscopy. Increments of blood pressure and the amount of a sedative drug were significantly lower in the n-ERCP group. ENBD was successfully performed succeeding to the n -ERCP in which mouth-to-nose transfer of the drainage tube was not required. CONCLUSION: n-ERCP is likely a well-tolerable method with less cardiovascular stress and no need of prior EGD or mouth-to-nose transfer of the ENBD tube However, a deliberate application is needed since its performance is difficult in some cases and is not feasible for some endoscopic treatments such as stenting.