Odontomas are hamartomatous lesions composed of mature enamel, dentin, and pulp, and may be compound or complex depending on the extent of morphodifferentiation or on their resemblance to normal teeth. They are the most common benign odontogenic tumours, constituting 22% of all odontogenic tumours of the jaw. They are often non-aggressive and slow growing in nature, and are usually diagnosed on routine radiological examinations in the second decade of life. We report the case of an unusually large, painless, complex odontoma, which is a rare entity. It was located in the left posterior mandible and was associated with missing 1st and 2nd left mandibular molars. The diagnosis was confirmed following surgical excision and histopathological analysis of the lesion.