This article investigates the nineteenth-century debate within transnational medical networks about the physiological effects of celibacy for priests. Many doctors, motivated in part by their animosity towards the Catholic Church, argued that the vow of celibacy was not only futile, but responsible for sexual immorality in the church. However, medical opinion was never uniform, and other doctors rallied to the church, defending the celibate vow as largely benign. Both sides shared a willingness to look abroad for support and inspiration. This article investigates this debate as a transnational phenomenon, as key texts were translated and published across Europe and North America, and as several notorious case-studies emerged to form the focus of international controversy.