As cognitive deficiencies in aged people constitute a growing factor in our societies, the possibilities for diagnosing dementia are described and analyzed critically. Based on a discussion of those changes in intellectual performance which are typical for normal aging (e.g., reduction in so-called fluid intelligence combined with preservation of so-called crystallized intelligence), the pathological forms of aging, especially Alzheimer's disease, are outlined. The present, internationally favored psychometrical measures for recording dementia in the aged and for evaluating and diagnosing it differentially are listed. Finally, certain requirements which have to be imposed on a diagnostic test for dementia are discussed.