We describe a case of adult onset Dandy-Walker syndrome. A 35-year-old woman presented with symptoms of increased intracranial pressure and cerebellar signs. After excision of the cyst wall of the posterior fossa. the patient recovered completely. The role of magnetic resonance imaging in establishing the diagnosis and following the course of operation are emphasized. Possible pathophysiological mechanisms involved in the late appearance of the clinical symptoms and the treatment of this anomaly are discussed.