[Cystic parosteal osteosarcoma. A case treated by resection].

A parosteal sarcoma in a twelve-year-old girl is described in which a large cystic lesion developed at the centre of the lower femoral metaphysis. Treatment was by extensive resection and reconstruction with an allograft in two stages. There was an excellent result after seven years. Only one other case was found in a review of the literature of slowly growing primary malignant tumours.