The NYU Women’s Health Study is a long-term observational study primarily funded by the National Cancer Institute. Between 1985 and 1991, the NYU Women’s Health Study enrolled 14,275 women at the Guttman Breast Diagnostic Institute in New York City for a study of endogenous hormones (hormones that are naturally produced by the body) and breast cancer. About 1500 women were also enrolled at the Strax Institute in Florida. At enrollment, each woman donated a blood sample and completed questionnaires. Blood samples are currently stored in –80 ° C freezers for subsequent laboratory analysis, allowing researchers to explore biological differences between women who develop disease and women who remain disease-free. Every few years, study participants are followed-up by mail or telephone and are asked to complete a questionnaire about their health conditions and lifestyle. From this information, the NYU Women’s Health Study is able to conduct different projects that examine the relationship between exposure to specific environmental factors and the development of chronic diseases.