In 10% of adult patients with hydrocephalus, the cause is because of aqueductal stenosis (AS), causing enlargement of the lateral and third ventricles. There are currently two alternate forms of surgical treatment for AS; shunt surgery and ventriculostomy. Shunt surgery is associated with high complication rates and many patients need revisions, but the effectiveness is high. Endoscopic third ventriculostomy (ETV), re-establishing a physiological route of CSF dynamics, has become the treatment of choice for AS in most neurosurgical centers. ETV has fewer complications and revisions are rare, but some patients need shunt surgery to improve despite a patent ventriculostomy. There are today no common criteria for patient selection to either ETV or ventriculo-peritoneal shunt surgery.