1. The detailed findings are presented of a woman aged fifty who had widely distributed ossifying skeletal tumours, the structure and form of which have been shown to be low-grade osteoblastic osteogenic sarcoma. The patient was treated with heavy doses of P³², to which is attributed some clinical improvement, but which induced a fatal aplastic anaemia.

2. The study of the several tumours, together with the history, the radiographs and the post-mortem findings, suggests that the lesions are multifocal skeletal primary tumours rather than numerous osseous metastases secondary to a solitary new growth in any one bone.

3. The focal neoplastic lesion is discussed in the light of personal experience of other osteogenic sarcomata of low grade but of solitary origin, and of the multifocal form of bone sarcoma which may complicate Paget's osteitis deformans.