This paper explores the impact of the concepts of identity and difference on demented persons (especially on persons with Alzheimer's disease). The diagnosis of dementia is often synonymous with the assertion that demented individuals are no longer capable of making reasonable decisions. But rationality is an important aspect of characterizing a person's identity. Hence, this prevailing image of dementia as a loss of self and a change of identity leads to the situation that demented persons represent difference and otherness. Here, the brain and the mind act as the source for difference. The paper discusses several identity concepts with regard to demented persons and the relationship between identity and difference in dementia. This analysis is accompanied by an examination of the current biopolitics of dementia and ageing as biopolitics constitutes the socio-political-medical understanding of dementia. Challenges and possibilities for dementia care will be explored in the context of this complex relationship between theoretical concepts and political, medical, and health-care practices.