From January 1979 to December 1985 356 patients underwent microsurgery for a ruptured intracranial aneurysm. 150 patients (42%) were operated on early, i.e. within 72 hours after subarachnoidal haemorrhage. 206 (58%) were operated on after this period. Both groups of patients were compared with one another in respect of preoperative staging (Hunt and Hess), localisation of the aneurysm, postoperative recovery (Glasgow-Outcome-Scale) and frequency of recurrent haemorrhages. 48% of the patients who were operated on early were preoperatively in stages I and II, 32% in stage III and 20% in stages IV and V. In the group of patients who were operated on late, 64.6% were in stages I and II, 17.5% in stage III and 17.9% in stages IV and V. 72.5% of the patients receiving early surgery in stages I to II showed a positive postoperative result (grades I and II of the Glasgow-Outcome-Scale = GOS) compared against 80.5% of those undergoing late surgery. 9.2% or 3.5% survived with considerable neurological deficits (GOS III). 18.3% or 15.4%, respectively, remained in the vegetative stage or died (GOS IV and V). A satisfactory postoperative result was obtained even in patients subjected to surgery in stages IV and V, in the following proportions: 40% if operated on early, and 48.6% if operated on late (GOS I and II). Aneurysms of the anterior communicating artery were most frequent, followed by aneurysms of the internal carotid artery and the middle cerebral artery.(ABSTRACT TRUNCATED AT 250 WORDS)