The Study of Women's Health Across the Nation (SWAN) is a multi-site, longitudinal, epidemiologic study designed to examine the health of women during their middle years. The study examines the physical, biological, psychological and social changes during this transitional period. The goal of SWAN's research is to help scientists, health care providers and women learn how mid-life experiences affect health and quality of life during aging. The study is co-sponsored by the National Institute on Aging (NIA), the National Institute of Nursing Research (NINR), the National Institutes of Health (NIH), Office of Research on Women's Health, and the National Center for Complementary and Alternative Medicine. Between 1996 and 1997, 3,302 participants joined SWAN through seven designated research centers. The research centers are located in the following communities: Ypsilanti and Inkster, MI (University of Michigan), Boston, MA (Massachusetts General Hospital), Chicago, IL (Rush Presbyterian-St. Luke's Medical Center), Alameda and Contra Costa County, CA (University of California Davis and Kaiser Permanente), Los Angeles, CA (University of California at Los Angeles), Hackensack, NJ (Hackensack University Medical Center), and Pittsburgh, PA (University of Pittsburgh). SWAN participants represent five racial/ethnic groups and a variety of backgrounds and cultures.