In this study, we examined the association between benzodiazepine use and the occurrence of Alzheimer disease and vascular dementia. The study was based on longitudinal data from a case-control study of 668 individuals aged 75 and older. The elderly were examined extensively by physicians, and family interviews were assessed. Dementia diagnosis was made by using DSM-III-R criteria. Individuals with a history of continuous use of benzodiazepines (BDZ+) were compared with nonusers (BDZ-), with respect to the incidence of Alzheimer disease or vascular dementia at follow-up 3 years later. It was found that there was a significantly lower incidence of Alzheimer disease in the BDZ+ group than in the BDZ- group. This negative association remained significant when controlling for age, gender, level of education, use of nonsteriodal antiinflammatory drugs, and estrogens. These results suggest that benzodiazepines may have protective effects against the disease.