Sarcoma complicating Paget's disease is uncommon; ninety-five cases have been collected and seven further cases are now reported. Sarcoma probably complicates less than 2 per cent of all cases of Paget's disease. There is a relatively high incidence in males, especially in the sixth decade, whereas bone sarcoma over the age of fifty years without osteitis deformans is rare. Injury is prominent in the history of many cases.

Comparison of Paget's sarcoma, "ordinary" bone sarcoma and the bones affected by uncomplicated osteitis deformans reveals some important differences. As to the type of tumour, osteogenic sarcoma is the commonest, but fibrosarcoma and round-cell sarcoma are also frequent.

The serum phosphatase is a most useful prognostic guide in a disease with a generally poor prognosis. Magnesium metabolism in relation to bone sarcoma requires further study.

Prophvlaxis is based on a clinical suspicion of this complication in Paget's disease, and measures are outlined which may be of assistance.

Sarcoma in Paget's bone is highly lethal, but Nature in striking down these old people may have provided us with facts which will ultimately solve problems common to all sarcomas of bone.