This observational, prospective study aims at evaluating how the occurrence of post-Endoscopic Retrograde CholangioPancreatography (ERCP) acute pancreatitis (PEP) could be influenced by difficult biliary cannulation that might be previously assessed by the morphological appearance of native major papilla in all the patients undergoing ERCP. The rate of successful biliary cannulation across papilla types could be used as intraprocedural quality and competence metrics during training. Moreover, recognizing difficult papillae could allow reserving those to experts to decrease the odds of failed cannulation.