Epidemiological study of old age mental disorders in the two rural areas of Japan.

Epidemiological investigations of mental disorders among the aged population were conducted in two rural areas of the southernmost prefecture of Japan. The population of the people aged 65 and over was 708 in Sashiki Village and 211 in Ikema Island. The prevalence of mental disorders among the aged inhabitants was 6.64% in Sashiki Village and 3.79% in Ikema Island. Dementia in the aging process was found in 5.36% in Sashiki Village and 2.37% in Ikema Island. All cases of dementia were of the simple type, except for a case with a paranoid state in Sashiki Village. There was no case of nonorganic psychotic conditions in both areas, except for the cases of schizophrenic psychosis whose onset occurred at an earlier age.