Odontomas are hamartomatous malformation of fully developed tooth structures like enamel, dentin and cementum.  These tumours are of two types, compound and complex depending on the basis of differentiation towards normal teeth. Of these complex odontomas are rare, asymptomatic and incidentally diagnosed on radiography. The tumours rarely present with large size causing facial asymmetry, inflammation and very rarely erupt into the oral cavity. Hence, herein we report the case of an unusual large complex composite odontoma erupting in the left posterior mandible of the oral cavity.