1. A father and two daughters suffering from Paget's disease are described.

2. The father's case is of special interest because he developed a malignant osteoclastoma of the mandible.

3. In the two daughters the condition was notable for the fact that in each case it began at the age of eighteen in the jaws, and led to the development of osteoporosis circumscripta of the skull.

4. The relationship between Paget's disease and osteoporosis circumscripta, and the age incidence and familial incidence of Paget's disease, are discussed.