The comparison between the overall results in series treated with late surgery and those obtained with early surgery demonstrates a marked reduction of mortality and an increase in good results in the series treated with early surgery. In many series in which a protocol of late surgery was employed no less than 10-15% percent of the patients died waiting for the operation.The advantage of early surgery is much more evident if the results are analysed on the basis of the Hunt-Hess grade on admission. In the past, some of the surgeons who considered early surgery an useful weapon for patients in Hunt-Hess I-II, thought that early surgery was too risky in Hunt-Hess III, and that grade IV and V patients should not undergo surgery.In Hunt-Hess III operative mortality and morbidity were respectively 15-30% and 10-25% with delayed surgery, but the overall mortality is up to 40% mainly due to the rebleeding rate. Operative result and overall outcome in Hunt-Hess III is much better in series treated in early surgery with Nimodipine, ventricular drainage and intracranial pressure control. In the past, the approach to Grade IV and V patient was usually nonoperative.This has changed today, since early surgical treatment is increasingly done also in these groups of patients. In our experience, the endovascular approach can be a good alternative in many cases. Such considerations are valid also for those patients, usually in severe clinical condition, with an intracerebral haematoma. Posterior circulation aneurysms have usually been operated on in late surgery.In these cases a careful selection of patients, the surgical approach and improvement in neurointensive care techniques to obtain more operating space and to minimize retraction, allow satisfactory results also with early surgery. Only a few series reported the results of early surgery in giant aneurysms. On the basis of those papers it can safely be affirmed that if the sac is clippable with the usual surgical technique, an early approach can be attempted. If temporary prolonged arterial occlusion or by-pass seem to be necessary, it is better to postpone surgery.