Congenital dilatation of the common bile duct or choledochal cyst is a rare condition which, until recently, was usually not recognized prior to operation. Although the number of reported cases is greater than 600, the group reported in this study may be the largest from a single institution in the United States. Ten patients with this anomaly were seen at the Childrens Hospital of Los Angeles during the two decades (1948-1968) among approximately 135,000 admissions. Clinical Series A summary of the clinical course of these ten children is found in the Table. Nine of the ten patients were females. The racial background of seven was white; two, oriental; and one, Negro. Five children developed the initial symptom during the first six months of life. In contrast, two were over 10 years of age at the time of the first recognition of their disease process. Six of the ten patients had