Periodontal disease is one of the most common chronic diseases in living populations, and most studies that have examined sex differences in periodontal disease have found higher frequencies in men compared to women. This study examines sex differences in periodontal disease in two cemeteries from medieval London: the East Smithfield cemetery (c. 1349–1350), an exclusively Black Death cemetery that represents catastrophic mortality (n = 161), and the St. Mary Graces cemetery (c. 1350–1538), a post-Black Death attritional assemblage that represents normal medieval mortality (n = 100). The results reveal a significantly higher frequency of periodontal disease, independent of age, among males compared with females in St. Mary Graces, but no significant difference between the sexes in East Smithfield. The sex differences in the attritional assemblage might reflect heightened susceptibility to periodontal disease in the living population or sex differences in frailty. The differences in the sex patterns of periodontal disease between the two cemeteries might be the result of disproportionately negative effects of the Great Bovine Pestilence and consequent decreases in dairy availability on female oral health among victims of the Black Death. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.