This paper offers a caution that emphasis upon the importance of mathematics in recent historiography is in danger of obscuring the historical fact that, for the most part, mathematics was not seen as important in the pre-modern period. The paper proceeds by following a single case study, and in so doing offers the first account of the mathematical writings of Jean Fernel (1497–1558), better known as a leading medical innovator of the 16th century. After establishing Fernel's early commitment to mathematics, (...) and attempt to forge a career as a cosmographer, it goes on to explain his abandonment of mathematics for a career in medicine. The ‘mathematization of the world picture’ is usually explained in terms of the perceived usefulness of mathematics, but Fernel's case shows that for many pre-modern thinkers mathematics was not regarded as a useful pursuit. The paper should serve as a reminder, therefore, that the take-up of mathematics by natural philosophers was by no means inevitable, but had to be carefully managed by early modern mathematical practitioners. The case of Fernel indicates that perhaps he was not the only would-be mathematical practitioner to abandon mathematics in favour of a calling that was more appreciated by contemporaries. (shrink)