Many observations indicate that women have a longer life expectancy than men. Population-based studies report that mortality and morbidity are higher in men than in women. The gender difference is constant in cardiovascular disease, cancer and dementia, the more frequent diseases in industrialized countries; these chronic conditions strongly influence longevity and quality of life in old persons. Biological, behavioral and environmental factors emerge as major contributors to the difference in mortality, morbidity and case fatality. However, the causes of gender differences remain poorly understood.