SummaryA case is reported of acromegaly, occuring in a 38 years old woman. Three years after the onset of the first signs, the patient developed a severe diabetes. The pituitary tumor was irradiated. Two months later, the patient suddenly was struck by a syndrome characteristic of cavernous sinus compression : this accident was interpreted as the result of an acute hemorrhage in the pituitary adenoma. Regression of the neurological symptoms was followed by complete disappearance of the diabetes (controled by blood sugar tolerance tests). The significance of this pathological experiment is examined in the light of recent knowledge concerning the influence of the pituitary in experimental diabetes.