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.

We conclude that conservative excision of the nail bed gives satisfactory results–89 per cent in this series. Recurrence is common but rarely causes symptoms. No patient had symptoms without recurrence. We think that recurrence is related to technique and to infection. Syme's terminal amputation is recommended for troublesome recurrence because repetition of Zadik's operation proved unsatisfactory.