Dementia is a declined state of cognitive functions which impair daily and social life mainly caused by progressive neurodegenerative disease, such as Alzheimer's disease(AD). The present study showed that about 15% of patients in Japan aged over 65 have dementia. The important point regarding the diagnosis of dementia is to detect it as early as possible. It is critical for the diagnosis to measure the indicators in blood and cerebrospinal fluid (CSF). Blood tests are useful to eliminate other factors that lead to cognitive decline derived from physical causes. CSF markers are significant for monitoring the existence and progression of neuropathologies. We need to accumulate extensive knowledge of the features, types, pathologies, development, and progress of dementia in order to assess patients and/or measured values.