Twenty-five patients with acromegaly were treated by transsphenoidal microsurgery. Fourteen patients (56%) were considered cured according to the following criteria: a. basal plasma GH less than 10 mU/l; b. glucose suppressed plasma GH less than or equal to 4 mU/l, and c. disappearance of TRH responsiveness if present preoperatively. Thirteen of the cured patients were re-evaluated after a mean follow-up period of 3.5 years (range 1.5 to 5.5 years). At that time, basal plasma GH was still less than 10 mU/l and glucose suppressed plasma GH was still less than or equal to 4 mU/l in all patients, indicating the practical value of our criteria. The remaining 11 patients (44%) received additional treatment by external pituitary irradiation and bromocriptine. Owing to surgery, 5 patients (20%) developed partial or panhypopituitarism.