Cognitive impairment without dementia is common in elderly persons and causes significant impairment in capacity to perform everyday activities. A number of nosological entities have been proposed for the classification of sub-clinical cognitive dysfunction. The more recent concepts assume an underlying organic condition, in particular the presence of early stage dementia. While prospective studies suggest that persons with mild cognitive disorder have a high risk of developing dementia, long-term follow-up of subjects with mild cognitive impairment suggests that dementia alone does not explain all cases. Cognitive disorder in the elderly must be construed as a common outcome for a number of interacting pathologies whose expression is also mediated by genetic, environmental and social factors.