Peru is a developing country in South America in a period of demographic transition. Peru has 28 million inhabitants, 49.8% of whom live in conditions of poverty. Life expectancy at birth is 71.2 years and elderly people (aged 60 years and over) constitute 7.7% of the population. The trend is for this percentage to increase and consequently for a greater prevalence of chronic age-related disorders such as dementia. Prior to the 10/66 Dementia Research Group study, there had been no other population-based studies of dementia in Peru. However, two important epidemiological mental health studies had been carried out in Peru by the National Institute of Mental Health “Honorio Delgado – Hideyo Noguchi”. In both, part of the survey was focused on the mental health of older people, those aged 60 years and over. One of the topics they examined was that of cognitive functioning among elderly individuals, surveys being carried out both in coastal cities and in the highlands in years 2002 and 2003 respectively. One thousand one hundred and seventy-two elderly people were evaluated using the Mini-Mental State Examination (MMSE) as a measure of cognitive function. More people in the highlands (50%) had cognitive impairment as measured by the MMSE when compared to the coastal cities (21.5%). This high prevalence of cognitive impairment in the highlands led them to divide the sample in two: Those with eight years of education and over and those with less than eight years and to reanalyze the results.