||This paper focuses on the relatively late emergence of psychiatric epidemiology as an international discipline, through local-global exchanges during the first 15 years of the World Health Organization (WHO). Building an epidemiological canon within WHO’s Mental Health Programme faced numerous obstacles. First, an idealist notion of mental health inherent in WHO’s own definition of health contributed to tensions around the object of psychiatric epidemiology. Second, the transfer of methods from medical epidemiology to research on mental disorders required mobilizing conceptual justifications, including a ‘contagion argument’. Third, epidemiological research at WHO was stymied by other public health needs, resource scarcity and cultural barriers. This history partly recapitulates the development of psychiatric epidemiology in North America and Europe, but is also shaped by concerns in the developing world, translated through first-world ‘experts’. Resolving the tensions arising from these obstacles allowed WHO to establish its international schizophrenia research, which in turn provided proof of concept for psychiatric epidemiology in the place of scepticism within and without psychiatry.