The brains of 3 adult subjects suffering from normotensive hydrocephalus have been examined pathologically. The diagnosis of normotensive hydrocephalus was based on clinical symptoms, pneumoencephalography and isotope cisternography, in 1 case integrated with the results of the constant-infusion manometric test. Part of the neuropathological findings were common to the 3 patients: leptomeningeal non-obstructive fibrosis, ventricular ependymal disruption, subependymal glial reaction, periventricular demyelination and spongiosis. Other neuropathological abnormalities were peculiar to each patient: leptomeningeal signs of previous subarachnoid haemorrhage; arteriosclerosis and multiple brain cystic infarcts; Alzheimer's plaques in the gray matter. The possible pathogenetic significance of the neuropathological findings summarized above in relation to the development of normotensive hydrocephalus is discussed.