This five year proposal to coordinate a prospective study of Menopausal Health in Aging Women builds on a unique combination of experience and expertise of the PI and her colleagues: 12 years conducting and analyzing the largest prospective study of menopause in North America; and extensive experience coordinating multi-site studies, including 8 current studies extending over 80 clinical sites, 5 of which are prospective, cohort studies. Two primary scientific aims are identified for this study, based on prior work. Aim I is to identify in a representative cohort of initially premenopausal women those variables that exhibit a distinctive pattern of change associated with menopause. Aim Il is to disentangle those changes that are clearly identifiable as associated with menopause (one or two points of inflexion in the rate of change) and those changes that are age-related, independent of the endocrinological changes that typify the menopause transition. To address these issues, the following core variables are proposed and linked in a research model: reproductive hormones, measures of blood pressure and lipids, blood glucose and insulin, anthropometry, and symptoms (including depression, hot flashes, mood swings). To address these aims, women who have menstruated in the prior 3 months with uterus and at least one ovary intact, are aged 40-47 (non-smokers) and 40-44 (smokers), are not taking hormone or other steroid therapies at baseline and from whom blood samples can be obtained will be recruited. Sample sizes for subgroup analyses and power to detect changes in trends for key variables are presented. Analytic strategies for continuous and categorical variables are discussed to address the scientific aims, including a discussion of missing and truncated data. A distributed data system; extensive quality control procedures; technical support to the clinical sites for cohort sampling strategies as well as for design and implementation of site-specific protocols and a proposal for disseminating results are fully described.