Odontoma is the most common odontogenic tumors. Although usually asymptomatic, it is often associated with tooth eruption disturbances. In exceptional cases, the odontoma erupts into the oral cavity. Approximately 20 cases of erupted odontoma have been reported in the literature. In contrast to the usual cases of odontoma, erupted odontoma may be painful with swelling and infection. Here, we report a case of erupted odontoma in the posterior mandible. The second molar was impacted, and its distal root was severely dilacerated. This case seems to be one of the largest erupted odontomas reported in the literature. However, despite its large size, the lesion had no associated symptoms. Of consideration is the association of this case with root dilaceration of the impacted second molar and the presence of maxillary peg laterals. Since the impacted second molar had the anomaly of dilaceration, its chance for eruption was minimal. Therefore, the odontoma was excised and the second molar was extracted.