RESUMEN
This paper discusses the differential diagnosis of an unusual calcified mass found in the pelvic cavity of 45+-year-old female excavated from 15th-18th century Lisbon (Portugal). The mass is relatively large, irregularly shaped, and exhibits a concave base with malformed teeth embedded within its inner surface. Considering its macroscopic and radiological characteristics, several conditions were considered in the differential diagnosis, namely eccyesis, fetus in fetu, lithopaedion, and ovarian teratoma. However, the morphological features of the specimen, such as its structure, morphology, and dimensions, are diagnostic of a teratoma. Its location and the sex of the individual are more specifically compatible with a calcified ovarian teratoma. With regional and temporal variations in the frequency of tumours, the report of new cases becomes imperative, especially from geographic regions where few cases have been identified. In fact, this appears to be the first case of ovarian teratoma detected in the Portuguese archaeological record and adds to the few palaeopathological cases described in the osteoarchaeological literature worldwide.