Occult hydrocephalus, also known as normal pressure hydrocephalus or normotensive hydrocephalus, is a term which has been applied to the syndrome in patients with communicating hydrocephalus and a CSF pressure of less than 180 mm of water. Although the syndrome may be associated with well-defined degenerative states, cerebro-vascular disease or with post-traumatic states, it: las been demonstrated that the CSF pressure can be normal in the presence of significant hydrocephalus. It is important to keep this condition in mind when undertaking a differential diagnosis of patients presenting with a mixture of fluctuating neurological signs and mental deterioration accompanied by urinary incontinence. The disease is reversible, with alleviation of all symptoms, provided .t is diagnosed and treated in its early stages.