Mammographic screening for breast cancer is a widely used public health approach, but is constantly a subject of controversy. Medical and historical research on this topic has been mainly conducted in Western Europe and North America. In Brazil, screening mammography has been an open topic of discussion and a challenge for health care and public health since the 1970s. Effectively, Brazilian public health agencies never implemented a nationwide population-based screening programme for breast cancer, despite the pressures of many specific groups such as advocacy associations and the implementation of local programmes. This article examines the complex process of incorporating mammography as a diagnostic tool and the debates towards implementing screening programmes in Brazil. We argue that debates about screening for breast malignancies, especially those conducted in the late twentieth and early twenty-first centuries, took place in a context of change and uncertainty in the Brazilian health field. These discussions were strongly affected both by tensions between the public and the private health care sectors during the formative period of a new Brazilian health system, and by the growing role of civil society actors. Our study investigates these tensions and their consequences. We use several medical sources that discussed the topic in Brazil, mainly specialised leading oncology journals published between 1950 and 2017, medical congress reports for the same period, books and theses, institutional documents and oral testimonies of health professionals, patients and associations collected in the framework of the ‘The History of Cancer’ project from the Oswaldo Cruz Foundation and Brazilian National Cancer Institute.