Two cases of Dandy-Walker syndrome are reported with emphasis on CT findings. The Dandy-Walker syndrome is known to be a developmental anomaly, which is a congenital cystic dilatation of the fourth ventricle due to atresia of foramen Magendie and possible also foramen Luschka, associated with some form of vermian dysgenesis. The CT findings of one case reveal huge cystic mass in midline of the posterior cranial fossa with small compressed cerebellar hemisphere in the lateral portion, associated with hydrocephalus. The other shows semilunar-shaped cystic mass in posterior cranial fossa with anteriorly displaced cerebellum, which communicates with apparent fourth ventricle through the vallecula. Both cases show no inferior.