1. The clinical features of hyperostosis cranii are briefly reviewed. In large series of cases the syndrome has been found to occur almost entirely in females.

2. In recent studies of dystrophia myotonica, it is apparent that hyperostosis cranii is one of the variable features of the disorder. This disease occurs equally among males and females and the hyperostosis cranii also is distributed equally among males and females.

3. Hyperostosis cranii also occurs in patients with Morgagni's syndrome, with acromegaly, and as "senile hyperostosis."

4. The etiology of hyperostosis is still a matter for speculation. More recent studies have focused attention on the endocrine system, and it seems probable, in view of the sex distribution in dystrophia myotonica, that the key to the problem may be found in this disorder.

5. In dystrophia myotonica the characteristic skull changes are hyperostosis cranii, a small pituitary fossa, excessive sinus formation and prognathism. These are acromegaloid changes. Gonadal atrophy is a common feature and endocrine study suggests that the endocrine defect is primarily a failure of the androgenic function of the adrenals and the testes.

6. In rodents and in humans ablation of the gonads leads to overactivity of gonadotrophic cells and, at times, of somatotrophic cells. Sometimes pituitary tumours develop.

7. Acromegaloid features may occur in eunuchs, and it is likely that the acromegaloid changes in dystrophia myotonica are of the same order from overactivity of growth hormone.

8. In animals excess of growth hormone produces thickening of the skull.

9. In dystrophia myotonica, acromegaly, and Morgagni's syndrome, it is suggested that hyperostosis cranii is an expression of unrestrained activity of growth hormone.

1. A report is given of a family suffering from dystrophia myotonica and familial Paget’s disease of bone.

2. Radiological changes in the skull occur in both disorders, which are quite dissimilar. Thickening of the calvarium, however, may be common to both.

3. The serum alkaline phosphatase is high in Paget's disease and normal in dystrophia myotonica.

4. In one patient the Paget's disease was complicated by the development of multiple sarcomata. Sarcomatous involvement of the vertebral column, observed in one of the cases, has not been recorded before.

Fourteen patients with dystrophia myotonica and a post-mortem report of another case are reported. All had radiological or other evidence of abnormalities of the skull. The most constant were a thickened calvarium, hyperostosis interna, small to very small pituitary fossa and extensive sinuses. It is believed that the high incidence of these changes cannot be coincidental and it is held that they should be accepted as some of the variable features of dystrophia myotonica.