Conventional radiographic and computer-assisted (CT) cisternography of the posterior fossa using Metrizamide was carried out in 25 and 33 patients respectively. The contrast medium was injected by the lumbar or cervical route. During conventional cisternography, contrast medium distribution is most easily controlled by a lateral injection at the level of the first to second cervical vertebra. Because of its physical properties, Metrizamide results in good demonstration of detail. CT cisternography is usually able to demonstrate an extra-cerebral space-occupying lesion with a diameter greater than 1 cm. This procedure has fewer complications due to the contrast medium or the technique, since small amounts of Metrizamide achieve an adequate increase in the density of the CSF; it is therefore possible to inject this by a lumbar route and to carry out the entire examination with the patient supine. Both conventional and CT cisternography permit very accurate diagnosis in the region of the foramen magnum. Both procedures can be used on their own or as an addition to conventional Metrizamide myelography.