The clinical characteristics and current concepts of pathophysiology of Cushing's syndrome have been reviewed. The specific type of pituitary or ectopic ACTH-dependent and ACTH-independent Cushing's syndrome and the underlying pathology can be determined biochemically and with the aid of anatomic localization procedures. Several approaches are available for treating pituitary ACTH-dependent Cushing's syndrome, but transsphenoidal pituitary microsurgery is the ideal type, with remission of the disease being observed in 80 to 90% of cases. When successful, pituitary microsurgery is followed by preservation of normal pituitary function and restoration of normal hypothalamic-pituitary-adrenal function within 6 to 12 months postoperatively. Medical therapy of Cushing's disease includes drugs that inhibit CRH-ACTH secretion, such as cyproheptadine and bromocriptine, and agents that inhibit cortisol synthesis, such as aminoglutethimide, metyrapone, ketoconazole, and mitotane, or that block the action of cortisol at the glucocorticoid receptor level, such as RU-485. With the exception of mitotane, which has adrenalytic effects, the action of the other pharmacologic agents is promptly reversed when treatment is discontinued. Thus, drug therapy is effective only as temporary treatment for Cushing's syndrome when surgical approaches are contraindicated or when attempts are made to improve the patient's clinical and metabolic status in preparation for surgery. Mitotane is effective in extending survival of patients with adrenal carcinoma, particularly when it is administered early as adjuvant therapy or when it is combined with repeated debulking resection of recurrent tumor. The toxicity associated with mitotane administration limits the use of larger and probably more effective doses in these patients. The synthesis of more specific cytochrome P-450 enzyme inhibitors and of mitotane analogues with more limited toxicity may ultimately provide more effective tools in the pharmacologic management of Cushing's syndrome.