Choledochocele or type III choledochal cyst is a rare abnormality of obscure etiology that consists of cystic or diverticular dilatation of the terminal intramural portion of the common bile duct protruding into the duodenum. It should be considered in the differential diagnosis of otherwise unexplained biliary colic or recurrent pancreatitis--particularly after cholecystectomy. An intraluminal duodenal filling defect on barium study that opacifies during cholangiography or endoscopic retrograde cholangiopancreatography is diagnostic. We present one case of choledochocele in which the first use of the biliary scintigraphic (HIDA) scan for diagnosis is demonstrated. An additional 47 cases found in the literature are reviewed and a new anatomic classification of choledochoceles is proposed as a guide for treatment. Treatment options are partial excision of the cyst, sphincterotomy, or both.