In 1965 Hakim and Adams described 6 patients with a mild impairment of the memory, slowness and paucity of thought and action, unsteadiness of gait and unwitling urinary incontinence.' These symptoms had evolved over a period of weeks or a few months. The pneumoencephalogram of these patients showed a quadriventricular hydrocephalus with no air in the cerebral sUbarachnoid spaces. A normal cerebrospinal fluid (CSF) pressure was measured by lumbar puncture. They all dramatically improved on CSF shunting. Hakim and Adams named this syndrome of symptomatic occult hydrocephalus with normal CSF pressure normal-pressure hydrocephalus (NPH). Afterwards many patients were described with the clinical triad of a gait disturbance, mental deterioration and urinary incontinence in combination with a communicating hydrocephalus on computed tomography and a normal CSF pressure. In studies on dementia NPH was found in 0% to 5.4% of the study population. NPH should be distinguished from acute hydrocephalus, in which CSF pressure is increased and headache, nausea, vomiting, and visual symptoms are present, and from chronic high-pressure hydrocephalus in which symptoms and signs of increased pressure are less pronounced. Symptomatic cases of NPH mainly follow sUbarachnoid hemorrhage, trauma, meningitis or intracranial surgery. Many cases, especially over the age of 60, have no known cause and are therefore idiopathic.