Previous studies have looked into the relationships between personality and dementia from three hypothetical points of views: 1) that personality type is a risk factor for dementia, 2) that personality changes occur before receiving a diagnosis of dementia, and 3) that premorbid personality traits define behavioral and psychological symptoms of dementia (BPSD) after receiving a diagnosis. This article overviews all three perspectives of the studies, after explaining the character and characteristic attributes of each perspective.