The radiological and clinical features of 90 histologically verified intraventricular masses were reviewed. Computed tomography (CT) and plain X-rays were available in all and angiograms in over half the cases. The localisation, effects on the adjacent brain substance and the presence and degree of hydrocephalus was evident on CT. Two-thirds of colloid cysts presented as pathognomonic anterior third ventricular hyperdense masses and the other third were isodense; an alternative diagnosis should be considered for low density masses in this situation. Plexus papillomas and carcinomas mainly involved the trigone and body of a lateral ventricle of young children and caused asymmetrical hydrocephalus; the third ventricle was occasionally affected also in children and the fourth ventricle more frequently and usually in adults. Two-thirds were hyperdense, one-third of mixed or lower density. The meningiomas were dense trigonal tumours of adults generally arising in the choroid plexus, but two tentorial meningiomas passed through the choroidal fissure and caused a predominantly intraventricular mass. Gliomas frequently thickened the septum and generally involved the frontal segments of the lateral ventricles. They may be supplied by perforating as well as by the choroidal arteries, which supply most other vascularised masses within the ventricles. Only 10% of our cases did not fall into one of the former categories; these included low density non-enhancing dermoid or epidermoid tumours and higher density enhancing metastatic or angiomatous masses.