Data on potential risk factors and current health status were collected with telephone interviews and self-completed questionnaires. Blood, urine, and environmental samples were collected and banked for future use in nested studies of women who develop breast cancer (or other diseases) and a sample of those who don't. The cohort is being followed prospectively for 10 or more years. Annual questionnaires update medical history and changes in exposures. About 300 new cases of breast cancer are expected to occur in the cohort each year. Analyses are ongoing and assess the independent and combined effects of environmental exposures and genetic polymorphisms that affect estrogen metabolism, DNA repair, and response to specific environmental exposures. Future analyses will focus on known and potential risk factors (e.g. smoking, occupational exposures, alcohol, diet, obesity) and include measurement of phthalates, phytoestrogens, insulin, growth factors, micro-nutrients, and genes. Women who develop breast cancer during the study are followed to assess the role of environment and genes in healthy survival following diagnosis and treatment. The cohort will also be used to explore risk for other diseases (e.g. heart disease, osteoporosis, other hormonal cancers, and autoimmune diseases) that are important for women.