Objective: Estimates of SLE incidence and prevalence in the United States have varied widely. The California Lupus Surveillance Project (CLSP) is funded by the Centers for Disease Control and Prevention (CDC) to determine credible estimates of SLE incidence and prevalence, with a special focus on Hispanics and Asians. Methods: The CLSP is a population-based registry of individuals with SLE residing in San Francisco County, California from 2007 - 2009. Data sources included hospitals, rheumatologists, nephrologists, commercial laboratories, and a state hospital discharge database. We abstracted medical records to define SLE cases as patients with documentation of > 4/11 of the American College of Rheumatology (ACR) Classification Criteria for SLE. We estimated crude and age-standardized incidence and prevalence, stratified by sex and race/ethnicity. Results: Overall age-standardized annual incidence rate was 4.6 per 100,000 person-years. The average annual period prevalence was 84.8 per 100,000 persons. The age-standardized incidence rate was 8.6 and 0.7 per 100,000 person-years in women and men respectively. It was highest among Black women (30.5), followed by Hispanic women (8.9), Asian women (7.2), and White women (5.3). The age-standardized prevalence in women per 100,000 was 458.1 in Blacks, 177.9 in Hispanics, 149.7 in Asians, and 109.8 in Whites. C-RC modeling estimated 33 additional incident and 147 additional prevalent cases. Conclusions: Comprehensive methods including intensive case finding provide more credible estimates of SLE in Hispanics and Asians, and confirm racial and ethnic disparities in SLE with the highest burden of disease in Black women, followed by Hispanic, Asian, and white women. Historical estimates of the incidence and prevalence of systemic lupus erythematosus (SLE) in the U.S. have varied widely (1). These differences stem from a variety of factors including the definition of SLE used, completeness of case ascertainment, geographic area, and racial/ethnic composition of the study population. The heterogeneity of disease manifestations and the lack of an accurate, reliable diagnostic test result in substantial challenges and costs to conducting large-scale epidemiologic studies in SLE. In an effort to develop more authoritative estimates of the incidence and prevalence of SLE, the Centers for Disease Control and Prevention (CDC) initially provided funding for two population-based lupus surveillance registries in Georgia (Georgia Lupus Registry) and Michigan (Michigan Lupus Epidemiology and Surveillance Program). These two registries have been successfully finished and focused primarily on Whites and Blacks (2, 3). To increase the reliability of SLE estimates in other racial/ethnic groups, the CDC funded two similar registries in California and New York to focus on Hispanics and Asians, and a third registry with the Indian Health Service to focus on American Indians and Alaskan Natives (4). In collaboration with the CDC and the California Department of Public Health, we conducted the California Lupus Surveillance Project to determine contemporary, populationbased estimates of the incidence and prevalence of SLE in San Francisco County during the period 2007 through 2009 using multiple methods of case ascertainment. A secondary goal was to describe the clinical and serologic spectrum of incident SLE in the population. To the greatest extent possible, we aligned our methodology with that of the Georgia and Michigan registries (2,3) to promote consistent data collection and optimal case ascertainment.