In this study, 55 patients with Cushing's syndrome (CS) (50 female, 5 male; mean age 34+/-12.3 yr) who attended our clinics between the years 1983 and 2000 were retrospectively evaluated for clinical and laboratory features and modalities and results of therapy, due to a few similar studies over the last ten years. Cushing's disease was diagnosed in 39 patients (71%), adrenal adenoma in 13 patients (23.6%) and adrenal carcinoma in 3 patients (5.5%). Centripedal obesity, moon face, hypertension, hirsutism and purplish stria were the most frequent findings. Loss of normal serum F circadian rhythm was found in all patients with CS. The overnight 1 mg oral dexamethasone suppression test and low-dose dexamethasone suppression test (LDDST) yielded 100% and 100% diagnostic sensitivity for CS, respectively. Sensitivity and specivity of the high-dose dexamethasone suppression test (HDDST) in distinguishing Cushing's disease was found to be 82% and 100%, respectively. All of the patients with adrenal CS were not suppressed with HDDST. Sellir CT and/or MRI accurately identified the tumor in 58% of these patients. Recurrence was observed in 3 (11%) of the 28 patients with Cushing's disease, treated by transsphenoidal adenomectomy. Recurrence was diagnosed 1.5, 3 and 6 yr after the operation in these 3 patients. One patient had residue tumor. In our case series, bilateral adrenalectomy plus pituitary irradiation achieved the highest remission rate (100%) in Cushing's disease. In 2 out of 4 patients (50%) treated by left adrenalectomy associated with pituitary irradiation, recurrence was observed. Panhypopituitarism due to tumor apoplexy was observed in one of the patients with Cushing's disease. All of the patients with adrenal CS, the tumor was accurately localized with imaging methods before the operation. The appropriate operative procedure resulted in complete remission in patients with adrenal adenoma. Consequently, Cushing's disease was the most common form of CS. The overnight 1 mg oral DST and 24-h urine free IF excretion (UFC) as screening tests, 2-day LDDST as diagnostic test and 2-day HDDST as differential diagnostic test were good studies. More successful outcomes have been achieved in treatment of Cushing's disease with the development of pituitary surgery in the recent years, as well as in our case series. Surgery is also curative for adrenal adenoma patients. Survival remains poor among carcinoma patients. ((C))2003, Editrice Kurtis.