Adrenalectomy for Cushing's syndrome due to adrenocortical adenoma was performed on 40 patients at Tokyo University Hospital between 1960 and 1990. There were 32 women and 8 men aged 2 to 59 (mean 35.7) years. Three different operative approaches to the adrenal gland were employed: lumbar approach in 24 cases, dorsal in 8, and transabdominal in 8 of whom 7 patients were operated before 1970 without definite preoperative localization of the lesions. Postoperative administration of cortisone and hydrocortisone as a steroid replacement has been reduced in duration and dosage in recent 10 years. Average treatment period was 3 years and 1 month in the 1970's, and 9.5 months in the 1980's, respectively. The mean daily dosage of steroid hormone was 517.5 mg (mean) on the operative day and 43.1 mg after three weeks in the 1970's, while 187.5 mg and 18.4 mg in the recent five years, respectively. Nonetheless, even in the recent 6 patients, metabolic alkalosis and hypopotassemia because of steroid excess were observed in a few days after the surgery. These observations indicate that period and dosage of steroid replacement have been reduced in these years and could be further shortened by means of rapid tapering in the early postoperative phase.