This paper describes an exceptional case of an enormous complex odontoma affecting the mandibular symphysis of a 9-year-old boy. Because of its dimensions, the lesion produced cortical bone expansion, dental displacement and impactation, which are clinical signs very seldom described for odontomas. The lesion was surgically excised in a conservative way using an intraoral approach with local anesthesia. After 7 years of follow up, all teeth had erupted and the mandibular bone healed totally. Because of its radiographic mixed radiolucent and radiopaque appearance and its expansive growth, it is imperative to make the differential diagnosis of giant complex odontoma for other more aggressive mixed odontogenic tumors, such as ameloblastic fibro-odontoma, odotoameloblastoma and cystic calcified odontogenic tumor. Conservative approach appears to be indicated in the treatment of such lesions.