Cholecystitis (ko-luh-sis-TIE-tis) is inflammation of the gallbladder. The gallbladder is a small, pear-shaped organ on the right side of the belly (abdomen), beneath the liver. The gallbladder holds a digestive fluid (bile) that's released into the small intestine. In most cases, gallstones blocking the tube leading out of the gallbladder cause cholecystitis. This results in a bile buildup that can cause inflammation. Other causes of cholecystitis include bile duct problems, tumors, serious illness and certain infections.