Hypothalamo-pituitary functions in 60 cases of Cushing's disease have been followed up after transsphenoidal selective adenomectomy. The adenoma was found and selectively removed in 56 cases. Remarkable clinical improvement followed within several months after selective adenomectomy in the successful cases, paralleled with endocrine results. Long follow-up studies demonstrated a recovery of the ACTH<ortisol system with restarting of the circadian rhythm and normal suppressibility to low-dose dexamethasone. The functions of the other anterior pituitary hormones such as GH, TSH, and gonadotropins also returned to normal after selective adenomectomy in the majority of the clinically cured cases. These results strongly suggest that transsphenoidal pituitary exploration should be accepted as an initial treatment of Cushing's disease because of its high clinical remission rate in association with fair chance of radical cure and return to normal endocrine function. ndocrinological studies by Orth and Liddle (1971) demonstrated that most cases of Cushing's syndrome were caused by hypersecretion of ACTH from the pituitary gland and approximately 25% caused by adrenal tumors and 16% by ectopic ACTH-producing tumors. Pathological changes of the sella turcica were, however, rarely found among the cases with apparent ACTH hypersecretion. Therefore, it had been generally believed that the true pathogenesis of Cushing's disease exists in the hypothalamus rather than in the pituitary itself. Contemporary operative results by transsphenoidal microsurgery have shown thata small adenoma does exist in many cases of ACTH-dependent Cushing's disease and clinical symptoms improved markedly by excision of an adenoma 6 ),7h I OI. 26 ),29),32). It sometimes happens, however, that an adenoma is not found through entire surgical procedures. In addition, there are some reports demonstrationg the presence of ACTH-cell hyperplasia in surgically excised specimens of the pituitary gland in Cushing's disease 20I ,25),27 1 • Therefore, some scholars still support the theory that the functional changes of hypothalamus or limbic system is the primary etiology. We have experienced transsphenoidal microsurgery in 60 patients with Cushing's disease. The following are the results of our experience. • ~~.,.~~~, .ill~~, ~.~~, ••~~. ~rr••