Tehran University of Medical Sciences Journal of Craniomaxillofacial Research 2345-5489 12 2 2025 09 23 118 122 Saeedeh Khalesi Dental Materials Research Center, Department of Oral and Maxillofacial Pathology, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran. Mohammad Parsa Ghazi School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran. Bijan Movahedian Attar Dental Implant Research Center, Department of Oral and Maxillofacial Pathology, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran. Sayed Mohammad Razavi Dental Implant Research Center, Department of Oral and Maxillofacial Pathology, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran. 2025 03 25 2025 07 25 Undifferentiated pleomorphic sarcoma is a common soft tissue sarcoma in the human body, but it is rarely reported in the oral cavity. This article aims to report a case of UPS in the mandible. An 83-year-old female patient was referred to the Department of Oral and Maxillofacial Pathology at the Faculty of Dentistry in Isfahan, Iran, with a complaint of sudden, painless swelling under her removable complete denture, which had grown gradually over three months. The size of the lesion was approximately 5cm, and there were no radiographic defects present. Neoplastic and malignant proliferation of cells, which is necessary for UPS final diagnosis, was present in the H&E microcopy evaluation. Furthermore, immunohistochemical examination proved that the lesion is an undifferentiated pleomorphic sarcoma. Because of the late diagnosis of the disease, the patient died due to lung metastasis before any treatment.  Keywords: Case report; Surgery; Undifferentiated pleomorphic sarcoma; Malignant fibrous histiocytoma. https://jcr.tums.ac.ir/index.php/jcr/article/view/534 https://jcr.tums.ac.ir/index.php/jcr/article/download/534/451