The common bile duct is a small, tube-like structure formed where the common hepatic duct and the cystic duct join. Its function is to carry bile from the gallbladder and conducts it into the upper part of the small intestine (the duodenum). The common bile duct is part of the biliary system. Bile, a yellow-brown fluid which helps break down fats in food, is produced by the liver. It is stored and concentrated in the gallbladder until it is needed to help digest food. When food enters the small intestine, the bile travels through the common bile duct to reach the duodenum. Gallstones are small, hard deposits which form inside the gallbladder when there is too much bilirubin or cholesterol in the bile. Although a person may have gallstones for many years without feeling any symptoms, gallstones can sometimes pass through the common bile duct, causing inflammation. If a gallstone blocks the common bile duct, it can cause choledocholithiasis. Symptoms of choledocholithiasis include pain in the right side of the abdomen (biliary colic), jaundice, and fever. Choledocholithiasis can be life-threatening if not diagnosed and treated immediately.