Background: Cognitive dysfunction is a common complaint associated with obstructive hydrocephalus. The purpose of this study was to determine the effect of endoscopic third ventriculostomy (ETV) on the neuropsychological outcome in patients presenting with cognitive decline and obstructive hydrocephalus. Methods: A retrospective review of patients who underwent ETV at the University of Calgary and had both pre and post operative neuropsychological testing, was completed. Presenting clinical features, etiology of hydrocephalus and ventricle size utilizing frontal occipital horn ratio was obtained. Outcomes and complications of the ETV were recorded. Detailed measures of intelligence, attention and concentration, executive function, visual and verbal memory, language functions and fine motor skills were completed. Post treatment change was determined utilizing Reliable Change Index. Results: A total of 13 patients were identified. Etiology of the hydrocephalus was aqueductal stenosis in 8 and tectal glioma in 4. The majority of patients (11 of 13, 85%) demonstrated cognitive dysfunction at the borderline (≤1 SD) or impairment level (≤1.5 SDs) in at least one domain. Nine patients (69%) showed reliable improvement in at least one cognitive domain. The greatest improvement was seen with visual memory (42%). One quarter to one third of patients demonstrated improvement on tests of intelligence quotient, verbal memory, attention and concentration, and executive function. Two patients declined in executive functioning. Ventricle size improved in eight patients. Conclusions: ETV is a safe effective procedure, capable of producing reliable improvements in cognitive dysfunction with hydrocephalus. Patients with cognitive complaints alone may benefit from ETV.