1. An unexplained case of extensive subperiosteal haematoma of the tibia is reported.

2. The radiological and biochemical findings are described.

1. Exostosis bursata in a patient with hereditary multiple exostoses is described.

2. Fracture of the tip of the exostosis had occurred causing acute pain and haemorrhage into the bursa.

3. Although it appeared that it might be a pseudo-joint cavity the histological appearance indicated that it was a bursa caused by friction between the exostosis and the surrounding soft tissue.