Overdrainage can be prevented or treated by implanting an anti-siphon device (ASD) or changing the opening pressure of the valve (OPV). Different ASDs have been developed since the first publication in 1973. They have in common that the lumen of the catheter is closed under influence of a negative hydrostatic pressure at the level of the ASD. The optimal valve setting for treating INPH is still the subject of controversy. The dilemma in INPH patients is that a low OPV might lead to overdrainage-related symptoms. A high valve setting might lead to underdrainage and the patient misses the chance of maximum improvement.