Normotensive hydrocephalus is a form of communicating hydrocephalus. It is characterised by a triad of symptoms referred to as the triad of Hakim: gait disturbance, impaired bladder control, and cognitive disorders. The symptoms are progressive in nature. The disease is usually observed in adults over 60 years of age. The paper presents the results of studies on cognitive function in patients with idiopathic (primary) hydrocephalus. Contrary to previous beliefs, cognitive disorders are not limited to executive dysfunctions. Impairment of psychomotor speed, attention, memory and visual-spatial functions is also observed. Neuropsychological diagnosis should differentiate idiopathic normotensive hydrocephalus from other diseases, including neurodegenerative ones, Alzheimer’s disease in particular. Idiopathic normotensive hydrocephalus is treated by implantation of a shunt system; however, research findings on improved cognitive function in patients after such treatment are inconclusive. Some studies point to significant global improvement in cognitive function, while other indicate changes in single domains. Comparison of results is difficult due to the differences in methodologies used and the time elapsed between the procedure and the measurement. Knowledge of the profile of cognitive disorders occurring in idiopathic normotensive hydrocephalus is important in the context of both neuropsychological diagnosis as well as neurosurgical qualification for shunt implantation. Surgery may improve functioning, but it may also involve the risk of multiple complications. Therefore, neuropsychological assessment proves helpful in the diagnosis and predicting surgical outcomes.