This article examines female sterilisation practices in early twentieth-century Rio de Janeiro, Brazil. It argues that the medical profession, particularly obstetricians and psychiatrists, used debates over the issue to solidify its moral and political standing during two political moments of Brazilian history: when the Brazilian government separated church and state in the 1890s and when Getúlio Vargas’s authoritarian regime of the late 1930s renewed alliances with the Catholic church. Shifting notions of gender, race, and heredity further shaped these debates. In the late nineteenth century, a unified medical profession believed that female sterilisation caused psychiatric degeneration in women. By the 1930s, however, the arrival of eugenics caused a divergence amongst physicians. Psychiatrists began supporting eugenic sterilisation to prevent degeneration – both psychiatric and racial. Obstetricians, while arguing that sterilisation no longer caused mental disturbances in women, rejected it as a eugenic practice in regard to race. For obstetricians, the separation of sex from motherhood was more dangerous than any racial ‘impurities’, both phenotypical and psychiatric. At the same time, a revitalised Brazilian Catholic church rejected eugenics and sterilisation point blank, and its renewed ties with the Vargas regime blocked the medical implementation of any eugenic sterilisation laws. Brazilian women, nonetheless, continued to access the procedure, regardless of the surrounding legal and medical proscriptions.