The preclinical stage of Alzheimer's disease is inconspicuous and there are - almost by definition - no reliable and valid symptoms and signs which would allow a very early diagnosis before the manifestation of irreversible deficits. For a clinical diagnosis of dementia, cognitive impairment has to be severe enough to compromise the activities of daily living. In the mild dementia stage, difficulties with declarative memory are usually prominent; depressive symptoms are not infrequent, but the patient usually manages to live alone. Supervision is needed in the moderate dementia stage, when other cognitive domains are affected in a more obvious manner and non-cognitive disturbances of thought, perception, affect, and behavior put increasing stress on the caregivers. Complete dependence of the patients, who frequently develop neurological disturbances, is typical of the late stage of illness. The life expectancy of patients with a clinical diagnosis of Alzheimer's disease is significantly reduced, but to date there is hope that the period of relative well-being and not of suffering can be prolonged with modern symptomatic treatment interventions.