In recent years attention has been drawn afresh to a group of cases in which there is a hyperostosis of the flat bones of the skull, associated with various mental changes and signs of endocrinological disturbances. In 1761 Morgagni mentioned the existence of hyperostosis of the inner table of the skull, and referred to its association with virilism and obesity. Morgagni's brilliant observation was neglected until recently, when it was proposed to name the condition Morgagni's syndrome. F. Morel (1931) published his monograph on frontal hyperostosis of the skull, and expressed the opinion that hyperostosis frontalis interna is a well-defined disease. He suggested that the proliferation of bone is provoked by adhesions between the dura and the inner table of the skull. As characteristics of the syndrome he described obesity, polyphagia, polydipsia, disturbance of sleep, weakness of muscles, loss of sight, headaches, and sometimes epileptic fits. In his opinion a pituitary disturbance is the primary cause of the disease. Shortly before Morel, R. M. Stewart (1928) described cases of insanity with localized calvarial hyperostosis. He found sclerosis of the anterior lobe of the pituitary, which he considered was the responsible cause. Schiff and Trelles (1931) suggested that there might be a relationship with Dercum's disease. Dressier (1927) and Greig (1928) dealt with the pathology of the bony changes. Greig suggests that a disturbance of the calcium and phosphorus metabolism is the causative agent. Critchley (1931), dealing with the neurology of old age, emphasized the importance of hyperostosis frontalis interna. A very extensive series of skulls taken from the average hospital population was investigated by Sherwood Moore (1936), 6,650 in all. In his case material there was 1.4 per cent. of hyperostosis. He tried to classify hyperostosis into four forms.