Osseous choristoma is a rare, benign lesion of the oral cavity occurring usually on the tongue. It appears as a tumorous mass of normal bony structure with mature cells in an ectopic position. Some lesions represent developmental malformations, whereas others may be reactive lesions, after trauma or chronic irritation. This is the first ever reported case of an osseous choristoma of the periodontium in the lingual aspect of posterior mandible.