This article analyzes the role of medical discourse in assessing the veracity of visionary experience in Golden Age Spain. Focusing on the Inquisition’s prosecution of suspected impostors, it describes the ways in which medicine could function as a tool of ecclesiastical discipline. The central argument is that by emphasizing the role of physiological factors in the genesis of many seemingly miraculous phenomena, church authorities used medicine as a way of controlling access to the supernatural realm in what amounted to a medical fideism.