We report the case of an odontogenic carcionsarcoma in a 9 year old girl. The tumour destroyed both buccal and lingual cortices of the right mandible. A mandibulectomy was performed, and the specimen was a fleshy fluctuant mass. Microscopic evaluation showed a biphasic appearance with malignant features of both the epithelial and fibroblastic components. The patient was never free of the disease from the point of surgery until she died 2 years 3 month later. This is the fifth case of odontogenic carsinosarcoma to be reported in the literature and the first case ever to be reported in a child.