This article addresses the historical process by which demographic growth was constructed as the "population question" in mid-twentieth-century Colombia. In other words, it addresses the mechanisms by which it was understood as a scientific, political and economic problem concerning the medical community, specifically the Colombian Association of Medical Schools (Ascofame). The paper demonstrates how this Association drew on notions such as demography, the idea of development as a path to well-being, and a broad definition of health to legitimize its authority and intervention in society. In its discussion of the historical construction of the "population issue", the article questions the use of quantitative methods as a tool to legitimize public and social action, and it reveals the subjective nature of quantitative description in demographic studies. Finally, it introduces the problem of the legitimate intervention of the medical practice not only in regards to its role in demonstrating the existence of the "population problem", but also in its ability to influence reproductive behavior in the quest for social transformation.