Freud’s ambivalent relations with medicine are well known. Based on his relatively unknown text, A religious experience, published in 1928, the authors present an analysis of the internal reasons for this conflict. Responding to a letter from an American doctor, who tells him about his reactions to an autopsy and the influence it had on his religious faith, Freud suggests an analysis that leads him to make a surprising slip. This slip reveals the conflicts inherent in the practice of autopsy, considered as a peculiar event in medical training that puts a strain on the future medical practitioner’s subjectivity. Based on the analysis of unconscious impulses and fantasmatic activity, the authors demonstrate that Freud’s theory is still surprisingly relevant today in the light of testimonies from contemporary doctors confronted with autopsy during their training or daily practice.