This article shows the decisive role that transnational dynamics played in the forensic recognition of silicosis. The causes of this occupational illness, the 20th century’s most mortal and which is progressing today in developing countries, were difficult to identify. The main reasons are the complexity of this disease’s classification and etiology, as well as the financial stakes that its compensation implicates for large industries (mines, foundries and Buildings and Public Works, notably). Official international organisations such as the International Labour Organisation and associations like the International Commission for Occupational Medicine are responsible for its recognition by having implemented an international forum dedicated to this matter between World War I and World War II. The results of which were a medical definition of this illness and its radiological identification, these included intentional imprecision and ambiguities: they alone would enable acceptation by employers. The case of silicosis reveals par excellence the negotiable character of work-related illnesses and the place formal and informal international exchanges hold in this process.