Normal pressure hydrocephalus (NPH) or, more precisely, chronic adult hydrocephalus, is a complex condition. Even if the basic mechanism is found in an impediment to CSF absorption, the underlying pathology is heterogeneous. In secondary NPH, the disruption of normal CSF pathways, following meningitis or sub-arachnoid haemorrhage, is responsible for ventricular dilatation. However, in about half of the cases, the etiology remains obscure. NPH is more frequently found in elderly people, probably in relation with the increased incidence of cerebrovascular disease. The diagnosis of NPH is based upon a triad of clinical symptoms. The main symptom is gait disturbances, followed by urinary incontinence and various degree of cognitive changes. The latter two symptoms are not prerequisites for the diagnosis. Radiological ventricular dilatation without cortical sulcal enlargement is a key factor, as well as substantial clinical improvement after CSF withdrawal (CSF tap test). Other CSF dynamic studies and various imaging investigations have been proposed to improve diagnostic accuracy, but no simple test can predict the results of CSF drainage. The current treatment is ventriculo-peritonial shunting, ideally using an adjustable valve. Results are directly dependent upon the accuracy of the preoperative diagnosis. Post-surgical complications may be observed in about 10% of cases.