The present Census is a checklist of the Greek medical manuscripts currently known in collections worldwide. It is both an amended and updated index of Diels’ catalogue, and a list of the items missed or overlooked in Diels, or located since. Although it does not supersede Diels’ catalogue, it is the indispensable instrument for a New Diels, and will be the reference for years to come for any new critical edition and medico-historical research based on manuscripts, besides providing the basis for a broad range of other historical inquiries, from codicology to the history of medicine and science, including Byzantine intellectual history, Renaissance studies and humanism, history of the book and early printing, and the history of medical philology and learning.