In the United States, women live longer than men, and they have lower death rates at virtually every age and for most causes of death. The sex differential in mortality has been increasing since the early 1900s, especially for those 15-24 and 55-64 years of age. Since 1970, however, that trend has slowed for persons 45-74, and for the first time, the sex differential among those 55-64 was actually smaller in 1980 than in 1970. While women have lower age-specific death rates than men for most causes of death, among adults 65 years old and older, the leading causes of death are the same for men and women: heart disease, cancer, and stroke. Despite their continuing mortality advantage, women generally experience more illness than men. They report more self-perceived poor health up to age 60. It has been frequently suggested that women may be more willing to acknowledge and report illness than men. Sex differences in illness among the elderly persist, however, when physical examinations are used for assessment of population-based samples. Injuries, one of the few conditions more common among men, are more common among women after age 55. Among the elderly, women appear to have more conditions that are disabling, such as arthritis, while men have more life-threatening conditions, such as heart disease. Women also use more health services than men, and they are institutionalized more frequently in their later years. Future health service planning must take into consideration women's greater health service needs. Future research needs to determine why women have more illness than men and whether women's greater life expectancy is associated with a greater active life expectancy, or if they are merely experiencing more years of disability and dependency.