A cyst or idiopathic cystic dilatation of the common duct is comparatively rare. The number of cases in an individual physician's experience is too small to formulate a definitive plan of treatment. The literature of the past is lacking in follow-up reports. Recent chemical methods for combating bleeding in cases of jaundice have possibly changed the surgical emergency of this condition. Most reported cases lack laboratory observations of the chemistry associated with jaundice. I have been able to collect 181 cases from the literature. Two additional cases are here reported from the Presbyterian Hospital. They are the only cases of the kind on file among the records of 757,000 cases. Many factors have been advanced as the cause of this condition. The most logical encountered is that given by Yotuyanagi, namely—the inequality of proliferation of the epithelial cells when the common duct is a solid cord of cells and