The fact that monstrous births were not represented in independent learned publications of the eighteenth century, except for the case of hermaphrodites, does not mean that the interest in them had disappeared or that they were no more considered proper objects of inquiry. This paper focuses on the medical understanding of monstrosity at the Royal Society of London. I point to the use of monstrous births in strengthening the authority of medical practitioners and lecturers. I also show some of their (...) uses in providing new questions for the scenes of medical inquiry of the period and as crucial evidence in the understanding of regular physiological phenomena. I discuss some of the reasons why monstrous formations continued to defy an 'Enlightenment' approach to nature based on the search for order and regularity. (shrink)