The ‘Sphere of Life and Death’ is an onomantic divinatory device present in around sixty-two manuscripts of late medieval English provenance. It is an example of illicit divination, and as such is condemned in various theological and legal tracts. However, at the same time, one of the most frequent manuscript contexts of this device is medical, as it claims to predict the life or death of a sick person. This article aims to show that the ‘Sphere’ was at the same time both licit medicine and illicit divination, and that we must take a less rigid approach to the categorization of such devices.