In this paper the author shows how 'Studies on Hysteria' ushered in a new century of psychiatry. While hysteria as a clinical entity remains as difficult as ever to define, the entire theoretical edifice of psychoanalysis rests upon it, as it allowed the discovery of the laws of conscious and unconscious thought and fantasy and thereby made it possible to explain symptoms and dreams. The author points out that many of the basic concepts of psychoanalysis are already to be found in the Studies and that, although some important ideas were thereafter forgotten, these have now come to be regarded as essential again. The notions of splitting and dissociation featured prominently in that seminal work and have now been reintegrated into mainstream theory. Present-day psychoanalysis is considered to have returned to its roots as embodied in the Studies, much less emphasis now being laid on the later concepts of drives, phases and libido theory. Female development and the woman's Oedipus complex are, in the author's view, as problematic as in Freud's day, perhaps because of his countertransference problems and neglect of the role of the mother, as exemplified in the Dora analysis. As the author shows, only the French analysts have remained consistently faithful to the concept of hysteria, whereas in other countries it no longer exists as a diagnosis. Yet the concept is stated to be important both historically and for clinical practice today.