This chapter centres on the medical career of Margaret Mason, Lady Mount Cashell (1773–1835). Mason is most often remembered as a marginal member of the Shelley circle and through her early relationship with pioneering women’s rights author Mary Wollstonecraft. Yet Mason’s significant late-life achievements as a medical student, a practising physician to the poor and an author of a domestic medical text are less well known. Mason’s Advice to Young Mothers on the Physical Education of Children (1823) pushed for women’s professionalization and education as a means of reconstituting and reimagining their traditional roles as midwives, a position which had been usurped by the male medical establishment throughout the second half of the eighteenth century. This chapter highlights how Mason’s writings intervened in scientific debates surrounding maternal health and positions her work within a small but important canon of woman-authored medical literature in the period.