This article is based on date collected in the medical dictionary of the French Acad?mie nationale de m?decine from the authors who are at the origin of the description of the diseases. The collection contains more than 2500 American authors who published their work in the 20th century. Our study allowed us the specify the origin of these American authors whom we divided into three groups: emigrants, second-generation immigrant's and U.S. born Americans. It appeared that the majority of the emigrants and second-generation immigrants were from Europe, mostly from the Eastern and Central Europe. A third of the emigrants and half of the second-generation immigrants were of Jewish ancestry and the immigration followed the pogrom, nazism and fascism. In the study of their scientific careers, it appeared that, compared to the US born Americans, both the immigrants and second-generation immigrants were recognized for the notoriety of their careers, through scientific and academic distinctions. This antisemitism favored medical-scientific immigration to the United States during the 20th century.