A case of common bile duct cyst operated upon in a 2 1/2 year old girl is used as a basic for discussing the forms associated with anomaly of convergence of common bile and wirsung's ducts. The latter, of dysembryoplastic origin, appears to be the cause of this type of cyst. These forms are atypical in that no mass is palpable and they are frequently complicated by a pancreatitis. They constitute the majority of Japanese cases when the anomaly is investigated. Its detection is possible by retrograde catheterization or more rarely during perioperative cholangiography, the only possibility in the very young infant. Different operative technics are outlined, taking into account principally the risk of secondary malignant changes and the possible performance of a hepatico-duodenal anastomosis without increasing the risk of an ascending angiocholitis.