The Aetiology of Hysteria (German: Über die Ätiologie der Hysterie) is a paper by Sigmund Freud about the sexual abuse of children below the age of puberty and its possible causation of mental illness in adults. Presented in April 1896, it is where Freud first outlined his seduction theory. [from Wikipedia]

In 1896, the young psychiatrist Sigmund Freud presented the first major paper he had ever written to his colleagues at Vienna's Society for Psychiatry and Neurology. Freud considered that his paper, entitled "The Aetiology of Hysteria," was of the utmost importance, since it proposed what he believed to be an irrefutable cause for the neuroses suffered by many of his patients. Quite simply, when listening sympathetically to his women patients, Freud had heard that as children they had suffered sexual assaults, and he believed that it was these acts of violence which had led to the victims' mental illness later in life.

The point of the paper was that sexually abused children, many of whom had come from "respectable" middle class homes, displayed significant "hysterias" later on in life—an observation that today would pass as obvious to the point of banality, but something that in 1896 provoked a backlash among Freud's older colleagues.

All the strange conditions under which the incongruous pair continue their love relations—on the one hand the adult, who cannot escape his share in the mutual dependence necessarily entailed by a sexual relationship, and who is at the same time armed with complete authority and the right to punish, and can exchange the one role for the other to the uninhibited satisfaction of his whims, and on the other hand the child, who in his helplessness is at the mercy of this arbitrary use of power, who is prematurely aroused to every kind of sensibility and exposed to every sort of disappointment, and whose exercise of the sexual performances assigned to him is often interrupted by his imperfect control of his natural needs—all these grotesque and yet tragic disparities distinctly mark the later development of the individual and of his neurosis, with countless permanent effects which deserve to be traced in the greatest detail.

In fact, as author and former Freud Archives Director Jeffrey Masson discussed at some length in his controversial bestseller The Assault On Truth: Freud's Suppression Of The Seduction Theory (1984), the pressure that was brought to bear on Freud was strong enough to make him change his mind completely about the validity of the sexual assault theory. In a dramatic about-face, he formulated his "seduction theory," in which children themselves became the seducers rather than the victims. [from Sigmund Freud and the Cover-Up of "The Aetiology of Hysteria" by Jonathan Eisen]