1. Two girls with non-familial osteogenesis imperfecta who subsequently developed osteosarcoma of the femur are described. One is of special interest in that there were multiple bone metastases.

2. It is suggested that the tumours arose spontaneously and were not related to the underlying bone disorder.

3. Because of the relative frequency of hyperplastic callus formation in osteogenesis imperfecta it is most important that adequate biopsy material of any suspicious lesion is examined because the early clinical picture may be indistinguishable from a tumour.