Introduction. Ageing is associated with the quasi exponential getting rip of dementia prevalence and incidence until SS Years, but the data in the oldest-old are controversial. Aim. Systematic review of population based studies that analyze prevalence and incidence of dementia in the oldest-old, specifically in nonagenarians. Patients and methods. Systematic review in Medline database of population based surveys describing prevalence or incidence in older than 90. published from 1998. 459 papers were identified, but of the 170 population-based detailed reviewed. 41 studies accomplished the inclusion criteria (Pamplona, Gerona and NEDICES Study are included). Results. 77 re dementia prevalence described in nonagenarians has a range (of 25-54%. The dementia incidence in older than 90 has a range: of 47-174 cases per 1,000 people/yerar, being greater in females. In the oldest-old a variable prevalence and incidence of dementia was described in the selected studies. Some authors consider that exist an exponential increase in the dementia prevalence and another wigs indicate c) slowing of. growth in nonagenarians. Conclusions. This review is concordant with a persistent not exponential increase in prevalence and incidence of dementia in nonagenarians. [REV NEUROL 2008; 47.: 347-54]