The authors have experienced 11 cases of radiologically or surgically proven choledochal cyst during theperiod of 4 years, and reviewed radiological and clinical features. The results are as follows: 1. The sex ratioof female to male was 2.7:1. Four were children under 10, and seven were adults over 30 years of age. 2. The mostfrequent symptom was abdominal pain (45%), which was followed by jaundice(36%) and palpable abdominal mass(27%).3. Morphologically, 4 cases were type A of Kimura classification (segmental cystic dilatation involving commonbile duct: pure type A of Kimura classification. 4. The union between the common bile and main pancreatic ductswas at high position in 5 of 6 patients in whom both ducts were adequately opacified with ERCP, PTC and/oroperative cholangiography, forming an abnormally long common channel. 5. Associated choledocholithiasis wasreported with increasing frequency. We experienced 4 cases(36.3%) which had multiple stones in the choledochalcyst. 6. Adenocarcinoma were combined in 2 patients: both were females of 38 and 45 years of age. 7. Ten caseswere correctly diagnosed preoperatively with ultrasonography. Specific ultrasound diagnosis of a choledochal cystcould be made by identifying two biel ducts entering into the large cyst which was separted from the gallbladderand extended deep onto the porta hepatis. Dilatation of intrahepatic ducts could be easily identified.