A neonate presented with Dandy-Walker syndrome manifesting as a large posterior cranial fossa cyst, aplasia of the lower cerebellar vermis, and elevation of the confluence of the sinuses but without hydrocephalus. A cystoperitoneal shunt was placed at one month after birth. The cyst diminished in size, and marked development of the cerebellar hemispheres and descent of the confluence of sinuses were observed, but not vermis development. The primary pathology of Dandy-Walker syndrome is posterior cranial fossa cyst formation due to passage obstruction in the fourth ventricle exit area and aplasia of the lower cerebellar vermis. The first choice of treatment in patients with Dandy-Walker syndrome in whom the cerebral aqueduct is open is cystoperitoneal shunt surgery, regardless of the presence or absence of hydrocephalus.