A series of adult patients with idiopathic hydrocephalus in whom shunts were placed are presented. Preoperative diagnostic and prognostic criteria were evaluated. Findings on computed tomographic scans (significant ventricular enlargement, the absence of gyral atrophy, and the absence of sylvian fissure enlargement) and the clinical triad associated with hydrocephalus in adults (dementia, ataxia, and especially incontinence of urine) all contributed individually and in combination to the diagnosis of hydrocephalus that could be corrected by surgery. The use of radionucleotide cisternography did not add any additional information. Its use as a diagnostic or prognostic aid is, therefore, suspect. The use of high-pressure shunting systems for the initial shunting procedure is emphasized.