A review of 177 patients with cerebral aneurysms is made, out of whom 106 with ruptured aneurysms were examined, whose operational timing and prognostic chances were well documented (group B, 1979-1982) and in part updated to 1984. Furthermore, relevant data of a previous series of 200 cases of cerebral aneurysm, treated between 1956-1978 were used (group A). The patients were graded according to Hunt and Hess, assessing the risks involved. The percentages of recurrent bleeding were in group A 36.5% and 28% in group B. The incidence of vasospasm (as seen in angiography) was in group B 39.6% (42/106 patients). The highest rate of vasospasm in the spasm group division B was found to occur in the second and third week after subarachnoid haemorrhage and amounted to 64.7% and 62.5%. A pre-operatively present vasospasm had no negative effects on the mortality rate, but influenced the outcome for the survivors effectively. The total mortality in group A was 22.5% and in group B 11.7%. Timing of the operation among patients in Hunt and Hess-grades I and II needs to discussion. The surgical position of patients in grade V is also certain. What remains to be discussed and needs attention is grade III and patients in grade IVa. Here the time of operative intervention must be planned individually depending on the course of the neurological status.