. This article presents an edition and translation of an Irish didactic poem found in a large compilation of remedies, charms and prayers that was written in the early sixteenth century by the Roscommon medical scribe Conla Mac an Leagha. The contents of this poem, and of the treatise in which it occurs more generally, are of inherent interest for our understanding of the history of medical learning in medieval Ireland. However, the poem is also of particular significance due to the fact that its penultimate stanza, which invokes the authority of one ‘Colmán mac Oililla’, is attested in two much later sources that provide insight into the transmission and reception of medieval Irish medical texts in the early nineteenth century, as well as into the relationship between manuscript, print and material culture during that period. The two sources in question, one of which is a previously unprovenanced signboard now kept in the Wellcome Collection in London, can both be connected with the work of the Munster ‘herb doctor’ Michael Casey (1752?–1830/31), who in 1825 advertised the publication of a new herbal containing cures derived from much earlier Irish-language medical manuscripts