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Objective. To estimate the prevalence of Behçet's disease (BD) in a multiethnic population living in France, with particular focus on disease risk among immigrants.Methods. The study was conducted in a county in the Paris metropolitan area that is home to 1,094,412 adults (ages >15 years), of whom 26% are of nonEuropean ancestry. Patients with BD living in this area during 2003 were identified using 3 sources (hospitals, community physicians, and the National Health Insurance database), and diagnoses were verified using the International Study Group criteria. Standardized, year-2003 prevalence rates were computed for the overall population and for each ethnic group. Stratified prevalence rates according to age at immigration to France were calculated to investigate the relationship between age at immigration and BD risk.Results. Seventy-nine subjects fulfilled our search criteria. The overall prevalence per 100,000 adults was 7.1 (95% confidence interval [95% CI] 3.5-14.4), and the prevalence for populations of European, North African, and Asian ancestry was 2.4 (95% CI 0.6-7.2), 34.6 (95% CI 24.4-47.5), and 17.5 (95% CI 10.7-27.2), respectively. Within the migrant population of either North African or Asian ancestry, BD prevalences were similar for residents born in France, residents <15 years old at immigration, and residents >15 years old at immigration.Conclusion. Our findings indicate that the prevalence of BD among immigrants of North African or Asian ancestry is significantly higher than that in the European-origin population, and comparable with rates reported from North Africa and Asia. Moreover, our results suggest that BD risk is not related to age at immigration. These findings support the hypothesis that BD has a primarily hereditary basis.