Idiopathic normal-pressure hydrocephalus remains difficult to treat. Controversy exists as to whether or not shunting can really improve cognitive functions and whether quantified intracranial pressure monitoring (ICP-Mo) can predict postoperative improvement rates. Several studies have drawn attention to the lack of a prospective study concerning the surgical outcome of this condition. We have performed such a study on idiopathic normal-pressure hydrocephalus patients shunted on the basis of ICP-Mo when "high" waves (amplitude > 9 mm Hg) were present. Twenty-three patients underwent surgery. The preoperative and postoperative clinical states were assessed by a quantitative procedure blind to the ICP-Mo results. A clear postshunting improvement was seen in 96% of the patients at 1 year with a statistically significant correlation between high wave relative frequency and the grade of improvement (P < 0.05). At the same time, 66.6% of shunted patients showed a significant improvement in cognitive functions. Complications of shunting were successfully managed without residual deficits in this series. We recommend the use of quantitative ICP-Mo as a criterion for surgery and to predict the improvement grade.