Prior to 1991, little research had focused on health issues unique to, or more common for, women. This was especially the case for studies of chronic diseases and their prevention in mature women. These conditions (coronary heart disease, cancer, and osteoporosis) are the leading causes of impairment of quality of life, morbidity, and mortality in post-menopausal United States women. The WHI, mandated by Congress, was established in 1991 by the National Institutes of Health and located in the Office of the Director (OD). The Clinical Coordinating Center for the clinical trial/observational study was funded in September 1992 and the 16 Vanguard Clinical Centers were funded in March 1993. The initial protocol was developed jointly by the Clinical Coordinating Center and the Program Office and was reviewed and approved by the Investigators Committee on April 20, 1993. Additional clinical centers were funded in 1994.