Twenty-two of 32 patients with Cushing's disease seen at the Mayo Clinic during a 3-year period were carefully studied radiologically (triaxial spiral tomograms of the sella and bilateral carotid arteriograms with magnification and subtraction techniques). Eighteen of these 22 pat-ents had radiologic evidence of small pituitary gland tumors and underwent transsphenoidal microsurgical exploration of the pituitary. A microadenoma (less than 10 mm) was found in 17 of the 18 patients. Hypercortisolism was corrected, and a clinical remission occurred in 16 of the 18 patients; the hypercortisolism persisted in 2 patients. A period of hypocortisolism occurred after removal of the pituitary tumor in all patients who experienced a remission. Remissions have been associated with normal anterior pituitary and adrenocortical function in a large percentage of patients who were adequately studied 6 months or more after pituitary surgery.