Osteoma is an uncommon benign osteogenic tumor characterized by the proliferation of compact and cancellous bone. The objective of this study was to report a case of osteoma in the basilar region of the mandible. The patient reported no pain, but the affected area was tender to touch and there was esthetic concern because of the apparent swelling. The mass measured approximately 5 cm in diameter and extended to the lingual area of the mandible. A vestibular approach was used for surgical treatment. After infiltration of a local anesthetic and vasoconstrictor, to expose the mandibular ramus, an incision was made with an electric scalpel along the external oblique ridge through the mucosa, submucosa and muscle, fascia and periosteum until the lower second molar, 3 to 5 mm inferior to the mucogingival junction. A mucoperiosteal flap was raised until the base of the mandible to access the tumor. Osteotomy was performed and the tumor was removed. The patient shows no recurrence of the tumor after 1 year and 6 months of follow-up. Periodical clinical and radiographic follow-up are satisfactory since recurrence is rare.