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 largecaliber 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 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.