To the Editor.— The report of biliary atresia in one identical twin is of interest. As the authors' state, the observation suggests that the malformation may be acquired rather than of genetic origin. Many pediatric pathologists consider biliary atresia an acquired defect in a large, but unknown, proportion of affected patients. The evidence to support the hypothesis is circumstantial. Stages of a presumed continuum from mild periportal inflammation and neonatal hepatitis to obstructive atresia have been found at autopsy in patients with the congenital rubella syndrome.2