A 69-year-old woman with a 15-year history of abnormal chest shadow was ref
erred to our hospital. An enhanced chest CT scan of the anterior mediastinu
m revealed a mass containing a high-density area. The preoperative radiolog
ic diagnosis was thymoma. Operation was performed in October 2000. Histolog
ically, multiple ossified areas were observed within the tumor. Intratumora
l ossification has never been reported in thymoma. Therefore, we report the
first case of thymoma associated with multiple foci of osseous metaplasia.