The present study aims to report a clinical case of a unilateral osteoma in a rare region and to discuss its clinical characteristics and possible forms of treatment for this lesion. In this clinical case the osteoma affected a mandibular coronary process, with a marked clinical characteristic, mushroom shape, causing zygomatic bone expansion and important limitation of buccal opening. The etiology of this lesion is unknown, but may present an association with infection, trauma, ionizing radiations, and hormonal and genetic influence. Osteoma can lead to an aesthetic complaint and, like coronoid process hyperplasia and osteochondroma, the osteoma can form a pseudoanquilosis; its treatment consists of surgical removal and osteoplasty. The treatment was satisfactorily performed through intraoral access, ostectomy, and osteoplasty.