The clinical condition normal pressure hydrocephalus (NPH) is one of the few conditions with dementia that can be successfully treated. Even though NPH was described more than 40 years ago, information on prevalence and incidence of this disease is scarce. The objective of this study was to obtain information about prevalence of iNPH in a Norwegian population. In a stable population of 220,000 inhabitants, structured and intensive efforts were directed towards the public via local newspapers, radio and television channels, and directed towards the healthcare professionals via personal letters and lectures, to recruit patients with idiopathic NPH (iNPH) investigation during a 12-month period. This population is served by only one neurological department and one neurosurgical department, thus avoiding any leakage of patients during the investigation period. We determined those patients fulfilling the diagnostic criteria of probable iNPH. Eighty-six patients were referred, of whom 48 patients fulfilled the diagnostic criteria of probable iNPH. This equals a minimum prevalence of iNPH in our population of 21.9/100,000. Most importantly, the prevalence was increasing with age. When excluding patients who had symptoms for more than 1 year, we found an incidence of 5.5/100,000/year. In this Norwegian population of 220,000 inhabitants, we found a prevalence of probable iNPH of 21.9/100,000 and an incidence of 5.5/100,000. The numbers should be regarded as minimum estimates.
