Transsphenoidal surgery has become the treatment of choice for Cushing's disease. In specialist centres, remission rates following transsphenoidal hypophysectomy of eighty per cent are being achieved. Immediate postoperative ACTH insufficiency (undetectable serum cortisol levels) is a valuable marker of successful removal of the pituitary lesion. This isolated ACTH deficiency of the pituitary is usually transient but may take months or years to remit. If postoperative cortisol levels are lower than preoperative levels and under 300nmol/l but not below 50nmol/l, the patient's condition will be improved although the patient will probably not be cured.
