In the etiology of dementia several genetic and various environmental factors are assumed to interact. Most epidemiological studies on risk factors have focused on "constitutional" factors like age, sex, birth order, dementia in the family and "life style" factors like smoking and alcohol consumption. Only few studies have investigated the role of psychosocial factors at work and during leisure time on the risk to develop dementia. Our paper gives a systematic review of all published results of controlled studies about psychosocial risk factors. A positive association has been observed between dementia and living alone, having no close social ties, not participating in social and leisure activities, and never having married. Recent studies have found that Alzheimer's disease in particular is negatively associated with diversity of activities and intensity of intellectual activities and positively associated with psychosocial inactivity, unproductive working style, living with a dominant spouse and with physical inactivity.