Five cases of the Dandy-Walker malformation are described using the magnetic resonance (MR) scan as a primary imaging technique. The patients' ages ranged from 34 weeks (in utero) to 41 years; their clinical and neuroanatomical characteristics encompassed the entire spectrum of the malformation. Clear visualization of the greatly enlarged posterior fossa, Dandy-Walker cyst, and absence of the inferior vermis established the pathological diagnosis and excluded other structural defects. In 3 patients, MR demonstration of the aqueduct and evidence of pressure on adjacent tissue aided in the surgical planning for ventricular decompression. The MR scan is a significant advancement in the radiological diagnosis of the Dandy-Walker malformation. The major technical advantage of the scan consists in its ability to delineate intracranial morphology in multiple planes.