The present study focuses on Freud's discovery of sexual aetiology in the period from his studies in Paris and Berlin (1885-86) to self-analysis (1897). The study gives a reassessment of both the link and the break between Freud's early works and the contemporary medical views and splits concerning sexual aetiology, which is relevant for the understanding of Freud's later developments. Freud's initial aversion toward sexual aetiology is investigated, and a significant connection between sexuality and death is found in the medical practice of female circumcision and castration in the treatment of hysteria. Finally, the relevance of the tabooed surgical operations is discussed in relation to a series of important moments for the birth of psychoanalysis (the collaboration with Fliess and the operation on Emma Eckstein, the Irma dream, the seduction theory and its abandonment, and the emergence in Freud of the memory of the death of little Julius as the “germ of guilt”).