Periampullary diverticulum has been frequently observed during endoscopic retrograde cholangiopancreatography (ERCP) in patients with variety of pancreato-biliary diseases including cholelithiasis. And it's close relation with biliary stones have been regarded as having clinical significances. Recently, periampullary diverticulum is also known to be associated with other pancreatico-biliary diseases and intestinal symptoms as well as cholelithiasis. The main aims of this study were to evaluate the association between periampullary diverticula and biliary stones according to their locations and characteristic morphology of the diverticulum and to determinate positive relationship between periampullary diverticulum and choledo-cholithiasis. We also want to find out the implication of the periampullary diverticulum on success and complication rate in performing the ERCP. We reviewed 99 of 497 cases having periampullary diverticulum on ERCP during past 3 years, and investigated size, location and number of periampullary diverticulum with special reference to the location of cholelithiasis. We also compared success rate and complication rate of ERCP in cases with or without periampullary diverticulum. The incidence of periampullary diverticulum was 19.9% (male: 18.9%, female: 21.7%) and increased after 50 years of age. As of anatomical characteristics of periampullary diverticulum, most of the diverticulum was single (84.8%). Size was usually smaller than 3cm (60.7%) and was attached with ampullar of Vater, type II in about half of cases (50.5%). Cholelithiasis was found in patients with periampullary diverticulum (68.7%, 68 cases out of 99 cases), and in patients without diverticulum (67.1%, 267 cases out of 398 cases). In patients with periampullary diverticulum, common bile duct stones was more frequently found (26.0%) than in the patients without diverticulum (14.8%), especially at type II (attaching type) lesions. Failure rate of ERCP was 11.1% with periampullary diverticulum and was 17.3% without it. These results indicate that periampullary diverticulum might be related with choledocholithiasis and does not seem to influence significantly in practicing ERCP.