Parosteal osteosarcoma, a subtype of juxtacortical osteosarcoma, has a better prognosis compared to central osteosarcoma with a relatively
low risk for recurrence and metastasis. Rarely, it can arise synchronously with other malignant tumors. Synchronous malignancies are
defined as the occurrence of a second primary malignancy within 6 months of the appearance of the first malignancy. Here in, we introduce
a 64-year-old woman who visited the Department of Oral & Maxillofacial Surgery, Yonsei University Dental Hospital with a 2 year history
of a whitish verrucous lesion on the palate. She presented an exophytic mass on mandible during the following visits. Histopathologic
evaluation revealed a synchronous parosteal osteosarcoma and squamous cell on right mandible and a precancerous verrucous leukoplakia
on the palate.