Expanding our knowledge of the history of dementia may be beneficial for its holistic understanding. This article aims to review the trajectory of the concepts of dementia in the world and Japan. Historical backgrounds of major dementia diseases are also addressed. The first reference to "imbecility" appeared in Greece in 6th century BC. A Japanese term "Mow-roku" (aged and devitalized) first appeared in 11th century, was replaced by "Chee-hou" (absent-minded imbecile) in 1960s, and then by "Ninchee-show" (cognitive impairment) in 2014 for humanistic reasons. In 1970s, dementia was delineated from normal aging, and the present concept of dementia was established.
Keywords: Chee-hou; Ninchee-show; dementia; dotage; imbecility.