Reconciling reported frequencies of periosteal reaction has been compromised by variable "criteria" for its recognition. One of the most important aspects of paleopathologic diagnosis is logical consideration of data, while avoiding biases introduced by preconceived notions. Documentation that skeletal manifestations of the treponemal diseases (as a population phenomena) are sufficiently (and reproducibly) distinct would allow meaningful assessment of the course of invasion and spread of treponemal disease in the Western Hemisphere. Quantitative assessment of the nature of osseous impact of specific treponemal diseases has resulted in identification of reproducible discriminating characteristics. The osseous reaction to treponemal infection, although reproducible for each variety, is not uniform among them. Examination of population frequency, demographics, character, and skeletal distribution of osseous treponemal impact provides clear, reproducible clues to the identity of the underlying treponematosis and help to distinguish them from other periosteal/cortical disorders. Application of the standard for distinguishing among the treponematoses has revealed only four patterns of disease: Those categorized as syphilis, yaws, bejel and a null pattern. The apparently inviolate categorization allows confidence in distinguishing among them