Epidemiologic studies of SLE performed as early as the 1960s have noted that SLE is not only more common, but also more severe among ethnic minority populations. Subsequent studies have generated vigorous debate over the extent to which genetic, environmental or other factors account for these differences. However, most epidemiologic studies of ethnicity and SLE treat ethnic groups as homogeneous categories, thus obliterating the genetic, cultural, and socioeconomic diversity that exists within groups that could contribute to the observed differences. Using genetic ancestry rather than self-identified ethnicity provides some advantages when investigating ethnicity, genetics, and disease characteristics. This approach does not assume that racial or ethnic groups are homogeneous but rather capitalizes on genetic heterogeneity within groups to more effectively dissect the relationship between ethnicity, genetics, and disease risk. The proposed project is designed to extend our genetic epidemiologic investigations of ancestry and SLE disease characteristics and will take advantage of a novel tool, the