Twenty-three untreated patients with acromegaly for 6-46 yr who were followed for 2-13 yr were studied. High resolution computed tomographic scans in 11 patients revealed herniation of the subarachnoidal space into the pituitary fossa (empty sella) and an intrasellar cyst in 2. Suprasellar tumor extension developed during the follow-up period in only 1 patient. Eleven patients previously (in 10 patients more than 4 yr earlier) had been treated with bromocriptine; 6 of these patients at follow-up had a solid intrasellar adenoma. Six of the patients with an empty sella or intrasellar cyst had had symptoms suggesting pituitary apoplexy. The sellar volume did not increase during follow-up in any patient with an empty sella. Plasma GH levels (basal and mean concentrations during an oral glucose load) increased (greater than 50 ng/ml) in 3 and decreased in 3 patients during follow-up. Normalization of plasma GH levels was rare, and physical well-being with complete absence of acromegalic symptoms was reported by only 4 patients. These results demonstrate that GH-secreting pituitary tumors may remain stationary for extended periods of time and that complete or partial disappearance occurs frequently, probably as a result of pituitary adenoma infarction.