Dementia is the most common mental disorder contributing greatly to disability, institutionalization, and shorter survival among the older population of both genders. Both the prevalence and incidence of dementia are higher in women than in men after the age of 80. Men and women have different profiles concerning risk factors and outcomes of dementia, with most of them favoring men. Epidemiological and experimental studies have indicated that estrogen would protect against dementia and Alzheimer's disease. However, evidence is still lacking that hormonal replacement therapy could protect against dementia. The role of male sex hormones for dementia risk has been less investigated. Although the causes of gender differences remain poorly understood, awareness of these differences may help identify persons at risk for dementia, affect its prognosis, and have implications for disease prevention.