Twenty patients with intracranial medulloblastoma were analyzed by CT. All patients presented with symptoms of headache, and in eight clinical findings consistent with intracranial hypertension were the only neurological abnormalities. In 16 cases, the medulloblastoma appeared as midline posterior fossa mass and in four cases it was located laterally in the cerebellar hemisphere. The fourth ventricle appeared abnormal and there was evidence of obstructive hydrocephalus in all cases. The lesion was hyperdense in 14 cases but in only one was there evidence of calcification; the neoplasm appeared isodense in six. Post-contrast enhancement was visualized in all cases; this was homogeneous in 18 and had a ring-pattern of variable thickness in two others.