In three cases of severe hypertension, in which total thyroidectomy had been done, death occurred as a result of rupture of the aorta. Although no notable change in the blood pressure occurred, the patients felt better, as a rule, immediately following the operation. In each case, varying degrees of chronic, idiopathic, aortic and arterial degeneration were found. It is suggested that this degeneration may result from a metabolic deficiency of aortic muscle under strain. It is suggested that there should be closer observation in such cases, in order to ascertain whether or not there is a relationship between disease of the glands of internal secretion and aortic and arterial disease. It is, of course, recognized that the induced hypothyroidism and aortic cystic degeneration might have been merely coincidental.