The natural course of clinically inapparent adrenal masses, most of which are benign cortical nonhypersecreting adenomas, is not yet defined. In the present study, 17 patients with adrenal incidentalomas, median diameter 2,0cm, range 1,0-4,0, 12 with normal adrenal function and 5 with subclini-cal Cushing's syndrome at diagnosis, were followed-up for 12-132 months, median 48, with a hormonal and morphological evaluation (CT scan) every 12-24 months. No patient developed overt endocrine disease. Autonomous cortisol hypersecretion at baseline was not a consistent finding during fol-low-up. An increase in mass size was found in 7 patients, with no signs of malignancy and a reduction in 3. These data indicate a growth tendency in a significant number of adrenal incidentalomas and an intermittent hyper-function in those showing subclinical autonomous cortisol hypersecretion.