As a progressive neuropathologic process, Alzheimer's disease is detectable already more than 20 years before the appearance of clinical symptoms. Magnetic resonance imaging is the tool for early diagnosis. Protein assays of the cerebrospinal fluid are available for differential diagnostic problem cases. While early diagnosis of patients suffering from mild cognitive impairment enables targeting of follow-up and medication to the patients in need thereof, the clinical use of biological markers for the recognition of the disease in symptomless patients is not considered allowed before effective registered drug therapy is available for the disease.