This lecture examines the history of a clinical case study of intersexuality in a woman that first appeared in Valparaíso, Chile in the early 1930s and later circulated to Spain and Germany. Crucial to the emergence of this case was the transnational circulation and Chilean reception of the work of Gregorio Marañon, a renowned Spanish clinician and intellectual who reached the apex of his scientific influence in the late 1920s for his account of “intersexual conditions” in humans. For the doctors treating woman in Valparaíso, the determination of her “true sex” was part of the larger project to identify and document Marañon’s intersexual types in the Chilean populace while modernizing the sexual politics of the state. Marañon’s formulation of his concept of intersexuality and its reception in Chile were both facilitated by the work of the Latvian-Chilean physiologist Alexander Lipschutz, a distinguished professor at the University of Concepción in southern Chile who had previously collaborated with leading figures in sexual science such as Eugen Steinach and Magnus Hirshfeld. The implantation of Lipschutz at the University of Concepción from 1926 to 1936 connected Chile to transnational networks of sexual science that created the conditions of possibility for the woman’s diagnosis and the circulation of her case back to Europe. As a study of transnational networks in the history of science and the history of sexuality in Latin America, this lecture reveals multidirectional flows of scientific knowledge between Latin America and Europe.