The most common benign tumors are osteomas and hemangiomas, whereas the most-common malignant lesions are osteogenic sarcomas. 2,3 Among them, a hard mass on the forehead is often suspicious of osteoma, but HO is rare.Heterotopic ossification refers to the structure of mature lamellar bone formed outside of the skeleton. Heterotopic ossification occurs as a complication after hip or knee surgery, and trauma, severe burns, or genetic disorders. 4,5 Craniomaxillofacial HO is uncommon and, in several reported cases, is primarily related to previous surgeries involving the masticatory muscles. [6][7][8] This case report is rare in that the clinical results expected based on the preoperative physical examination and MRI of the tumor were slightly different from the histological biopsy. Although the MRI results showed calcified granuloma, in fact, HO was found on histological examination after surgery. Moreover, it was unusual that the mass was in the supraperiosteal.This case suggests that HO can develop on the forehead without any other clinical history, including surgery or trauma. Furthermore, the location of the bone mass may, in rare, be located in the supraperiosteal.