Endoscopic retrograde cholangiopancreatography (ERCP) is endoscopy of the biliary tree and the pancreatic duct . By injection of contrast media, a retrograde image of both structures can be formed on X-ray, facilitating the diagnosis of obstruction, e.g. by gallstones or cholangiocarcinoma.

The patient is lightly sedated similar to colonoscopy. Then a flexible camera (endoscope) is inserted through the mouth, down the esophagus, into the stomach, through the pylorus into the 2nd portion of the duodenum where the sphincter of Odi (the opening of the common bile duct) exists. The region can be directly visualized with the endoscopic camera while various procedures are performed. Sometimes a wire with a balloon is passed into the bile duct, then inflated in order to expand the opening of the bile duct to allow passage of gall stones. Occasionally, an electric cauterizer will be used to cut the sphincter opening, making it wider. The test can also be diagnostic in that dye can be introduced, and followed using a fluoroscope, to look for blockages, or leakage of bile into the peritoneum (the abdominal cavity).

Potential complications include acute pancreatitis and perforation.