100 patients with a known history of choledocholithiasis were selected. The main reasons for performing ERCP were the presence of severe jaundice or insufficient information obtained with intravenous cholangiography. Analysis is made of the various complications due to the presence of common bile duct stones. A surprisingly high incidence of choledochoduodenal fistulas was seen; two types of such fistulas can be recognized. A brief discussion is given of etiological factors involved. ERCP is also very useful in the evaluation of surgical anastomosis and complications due to surgery such as narrowing or complete ligation of the common bile duct. Finally, pancreatitis, another complication of choledocholithiasis, is evaluated with ERCP, showing the importance of reflux from the common bile duct into the pancreatic ducts in the etiology of this condition.