To determine the prevalence, genetic and environmental determinants, and potential clinical, personal, and societal impact of iron overload and hereditary hemochromatosis, in a multi-center, multiethnic, primary care-based sample of 100,000 adults. The study is conducted by the Division of Epidemiology and Clinical Applications of the NHLBI, the Division of Blood Diseases and Resources of the NHLBI, and the Ethical, Legal, and Social Implications (ELSI) Research Program of the NHGRI.