This case study describes and provides a differential diagnosis for a femoral lesion. Individual M81 was a young adult male from Milicz, a 12^th–13^th century cemetery, and a subsection of the osteological collection curated by the Polish Academy of Sciences in Wrocław, Poland. The skeleton underwent standard anthropological analysis to estimate age‐at‐death and sex. The lesion was then evaluated through macroscopic and radiographic analyses, using clinical and paleopathological criteria. The right femur presented with abnormal bone contouring at the proximal metaphysis. A radiograph revealed a round, osteolytic lesion with a thin sclerotic border, located parallel to the long axis of the bone. The radiographic appearance of the lesion, along with the individual's estimated age‐at‐death and sex, lend to a differential diagnosis of a simple bone cyst. In paleopathology, there have been scant reports of cystic lesions and fewer reports of simple bone cysts. This case adds further data to a clinically common, yet underreported, pathology and may be the first case of a simple bone cyst reported from a Polish context.