This article explores the research project that led to the development of facial feminization surgery, a set of bone and soft tissue reconstructive surgical procedures intended to feminize the faces of male-to-female trans- women. Conducted by a pioneering surgeon in the mid-1980s, this research consisted of three steps: (1) assessments of sexual differences of the skull taken from early 20th-century physical anthropology, (2) the application of statistical analyses taken from late 20th-century orthodontic research, and (3) the vetting of this new morphological and metric knowledge in a dry skull collection. When the ‘feminine type’ of early 20th-century physical anthropology was made to articulate with the ‘female mean’ of 1970s’ statistical analysis, these two very different epistemological artifacts worked together to produce something new: a singular model of a distinctively female skull. In this article, I show how the development of facial feminization surgery worked across epistemic styles, transforming historically racialized and gendered descriptions of sex difference into contemporary surgical prescriptions for sex change. Fundamental to this transformation was an explicit invocation of the scientific origins of facial sexual dimorphism, a claim that frames surgical sex change of the face as not only possible, but objectively certain.