Odontomas as a group are the most common odontogenic neoplasms. They are mixed lesions containing fully formatted dental tissues, both epithelial and mesenchymal, and are usually found during a routine radiographic examination or as a factor in noneruption. Odontomas can be divided into two types: the complex and the compound odontoma. Both types are composed of enamel, dentin, cementum and pulp tissues, but in complex odontomas the tissues are arranged in a haphazard fashion with no discernible dental structures, whereas in compound odontomas the dental tissues exist in a more regular pattern so that the lesion consists of tooth-like structures. We report a case of a 23-year-old man with a large complex odontoma involving the left maxilla and maxillary sinus with clinical, radiographic and histological findings. Because of the size of the mass and its clinical course, benign neoplasms were considered in the differential diagnosis. Surgery was the treatment of choice, and recurrence of the lesion is not expected.