This paper uses macroscopic and radiological examinations to provide differential diagnoses of pathological lesions in the skeleton of a young woman, 20-25 years of age, which triggered the Danish palaeopathologist Vilhelm Møller-Christensen's interest in leprosy. The skeleton was incomplete, but the majority of bones of the upper body, as well as the skull, were present. The pathological changes consisted of medullary and cortical lytic foci, periosteal reaction and enhanced cortical density. The lesions were most extensive on the left side, especially around the elbow, wrist and scapula. Treponematosis, leprosy, smallpox, ergotism, rheumatoid arthritis, tuberculosis and sarcoidosis are all reviewed with regard to bone and joint pathology and their likelihood of being the correct diagnosis. We concluded that the most plausible diagnosis is treponematosis, but neither sarcoidosis nor smallpox can be completely excluded.