Population-based research is possible in this setting because medical care for residents of Olmsted County, MN is largely self-contained within the community and is delivered by a small number of providers. Most care is provided by the Mayo Clinic, which has maintained a common medical record with its two large affiliated hospitals for over 90 years. This dossier-type record contains both inpatient and outpatient data and is easily retrieved for review because the diagnoses and surgical procedures entered into these records are indexed. Mayo Clinic supports the index and maintains its 6 million patient dossiers in their original form. Through the Rochester Epidemiology Project, medical records of the other providers in the area are indexed into the same system and can also be retrieved for IRB-approved studies. Consequently, the details of the medical care provided to residents of the community are available for study, thus insuring virtually complete ascertainment of major illnesses for this delineated population. This resource can be used for descriptive epidemiological studies of disease incidence or prevalence, for retrospective cohort studies of disease progression and/or outcomes based on these inception cohorts of unselected patients from the community and for population-based case-control studies of the determinants of disease. Dr. Melton's work has focused on the epidemiology of chronic diseases, especially osteoporosis and fractures, and has led to over 500 peer-reviewed publications to date. Current emphasis is on defining fracture risk in the population using state-of-the-art quantitative tomography assessments of bone strength in the hip, spine and wrist.