Epidemiologic studies establish a pattern of disease occurrence that predicts annual incidence (the number of new cases per year in a defined population), prevalence (the total number of cases in a defined population), and mortality. If this pattern changes over time or within certain groups, the assumption can be made that causal factors for disease expression are also changing. This information can lead to the development of testable hypotheses regarding disease causation and disease registries can provide a population for study. The autoimmune diseases are relatively rare, presenting a challenge to the epidemiologist. The Scleroderma Registry is a population-based census of systemic sclerosis in the Detroit, MI, area established to determine these baseline epidemiology parameters and to provide a framework to study this disease.