Between the years of 1999 and 2001, during the excavation of the Praça da Figueira (Lisbon, Portugal), several human osteological remains from various chronological periods were discovered. Amongst them several skeletons are known to be related with the Hospital Real de Todos-os-Santos (Royal Hospital of All Saints - RHAS), which had an important role. The hospital history begun in 1492 and ended in 1755 largely as a consequence of the Lisbon earthquake. Of the skeletons exhumed, one in particular, the adult female Sk. 1310 showed significant pathological changes. The bone lesions characterized by new bone deposition, with a symmetric and disseminate pattern, were found in the upper limbs, distal end of femurs and in tibia and fibula diaphyses. A bowing deformity with "sabre shape" morphology was also observed in the tibiae. The most striking lesions, characterized by healed nodular cavitations and similar to those of caries sicca, were recorded on the frontal bone. Considering the value of a complete description, as well as the application of multiple lines of enquiry for a reliable differential diagnosis, three distinct techniques were applied and compared: visual examination, imagiology and histology. The results showed that the macroscopic analysis coupled with conventional X-ray analysis were fundamental to obtain a possible diagnosis of acquired syphilis. In contrast, the CT-scan and the histological analyses were less informative. The application of a new scoring system also supports a diagnosis of acquired syphilis. This case-study constitutes the first evidence of syphilis associated with the RHAS, supporting historical data on the pivotal role that this hospital had on the treatment of several conditions, namely, syphilis.