The gallbladder is a small muscular pouch in which bile is stored. It is located on the upper right side of the abdomen, attached to the lower surface of the liver and connected to the liver and the duodenum by the bile duct. The duodenum is the part of the small intestine, into which bile is released to aid in fat and vitamin digestion. Gallstones are crystelline concretions in the gallbladder or in the bile ducts. They can vary in size and shape from as small as a grain of sand to as large as a golf ball. They consist mainly of bilirubin, cholesterol, and calcium salts. The gallbladder may contain a single large stone or many smaller ones.