The development of transsphenoidal microsurgery and the refinement of endocrinological and radiological diagnostic procedures have afforded therapeutic options appropriate to the individual case in patients with hypercortisolism. The present series of 100 cases is derived from 104 patients with the diagnosis of Cushing's disease who underwent transsphenoidal pituitary exploration between 1974 and 1981. Excluding four patients in whom the pituitary gland was not exposed because of intraoperative technical difficulties, an overall cure rate of 78% was achieved. Among 71 patients with tumors confined to the sella turcica, 87% had correction of their hypercortisolism, 11% represented therapeutic failures, and one patient had tumor recurrence. In contrast, among 25 patients with extrasellar extension, correction of hypercortisolism was achieved in only 48%, 40% failed to respond, and 12% of the patients had recurrence. Four patients who failed to respond to total hypophysectomy have ectopic sources of adenocorticotropic hormone. The results indicate that transsphenoidal microsurgical exploration for a basophilic adenoma is the procedure of choice in adults and children with Cushing's disease. The diagnostic and surgical approach to these tumors, as well as pitfalls in the transsphenoidal treatment of Cushing's disease, are discussed.