The purpose of this study was to clarify the prognosis of senile dementia based on a 5-year follow-up study in institutions for the elderly. The subjects consisted of 747 cases over 60 years of age. Of these 316 cases showed clinical dementia but 431 cases had no intellectual disturbance in July, 1987. The mortality rate (56.3%) of the demented group was significantly higher than that (31.8%) of the non-demented group. The mortality rate of patients increased with aging. However, the mortality rate of the demented group did not correlate with the severity of dementia. An autopsy study revealed that the direct causes of death in 51.1% of demented patients were pneumonia and cardiovascular diseases. Among the demented patients followed up for 5 years, 22.5% showed severe worsening of dementia, 25.8% showed slight or moderate degree of worsening and 51.7% showed no change. Factors causing exacerbation of dementia included cerebrovascular disease and bone fracture.