Endoscopic retrograde cholangiopancreatography (ERCP) is an advanced therapeutic procedure to manage choledocholithiasis and pancreatobiliary malignancy. On occasion, ERCP failure is encountered due to difficulties in cannulation. We assessed the safety and feasibility of cap-assisted ERCP via analyzing cases in which cannulation was complicated by periampullary diverticulum. Between November 2013 and March 2014, ERCP procedures were performed in 346 patients in our tertiary medical center. Among the 73 patients who had a periampullary diverticulum, conventional ERCP failed in 5 patients due to hidden papilla (n=3) or use of tangential approach (n=2). As a rescue method, needle knife fistulotomy and selective biliary cannulation using cap-fitted forward-viewing endoscopy were successfully used in 4 patients without major complications. Based on our experience, cap-fitted forward-viewing endoscopy was relatively easy to measure the exact position of papilla and to perform biliary cannulation properly. Therefore, we recommend using cap-assisted ERCP by forward-viewing endoscopy as a useful and safe alternative to manage patients in whom cannulation is complicated by periampullary diverticulum.