Three patients with hydrocephalus aged 16, 26, and 33 years demonstrated memory deficits before or after the insertion of a ventricular shunt but at no time demonstrated ataxia, incontinence, or dementia. Following shunt surgery, memory functions improved rapidly in the patient who had had a recent acute onset of hydrocephalus, but in the two patients with a long period of hydrocephalus before shunting, memory impairments did not recover significantly in one patient, and in the other, memory impairments had become more severe by 12 months postshunt. Other neuropsychological and psychological sequelae of adult hydrocephalus are discussed, and it is suggested that for patients with chronic hydrocephalus, an extended period of neurological and neuropsychological monitoring may be advantageous before a decision is made to perform shunt surgery.