Epidemiology of mental disorders emerged in the post-1945 era at the intersections of different areas of knowledge. Given its ambitions, the Stirling County Study provides an instructive case study. It is also a good example of how the epidemiology applied methodological skills from social sciences. This paper aims, first, to reconstruct one of the first episodes in the development of psychiatric epidemiology. Its second purpose is to provide a detailed description of interdisciplinarity at work, and to examine its effects. After explaining some of the major features of the Stirling County Study, I emphasize the links between some of the first results, particularly regarding young people as a population at risk, and the job market after the Great Depression. [ABSTRACT FROM AUTHOR]