The proposed objective is to understand the appropriations and scientific transpositions between mental hygiene as a technical solution and eugenics as an ideology, in the emergence of the concept of mental health in Ibero-America. Inscribed in the current of the social history of medicine, a documentary investigation, through heuristics and hermeneutics archives. Inquiring about the emergence and extension of mental hygiene leagues in these regions, allows us to verify that there were discursive and practical convergences between the institutions that promoted eugenics, mental hygiene and psychotechnics. It is noted that, in the first half of the twentieth century, the leagues had in common their origin and functioning in neuropsychiatry associations, also a close relationship of both with eugenics societies. Similarly, all of these formed a section of childcare and, at the same time, the societies of this specialty along with those of pediatrics included a section of eugenics. There was a social turn of prevention, deployed by disciplines and policies, such as the “social issue of health”, hygiene, social medicine, and
psychology. In this process of extension to the population, social psychiatry emerged, a field that stood out most in Ibero-America during the twentieth century.