The optimal timing of definitive aneurysm repair following subarachnoid hemorrhage remains a controversial issue. In order to examine whether the timing of surgery alters the incidence of certain technical difficulties and complications associated with intracranial aneurysm repair, data from two recent co-operative studies were examined. The cases submitted to the International Co-operative Study on Timing of Aneurysm Surgery by the University of Toronto hospitals, and the cases submitted from multiple centres to the Three-Dose Multicentre Randomized Double-Blind Nimodipine Study were evaluated with regard to operative difficulties and complications, comparing early (less than or equal to 3 days) and late (greater than or equal to 4 days) surgery following subarachnoid hemorrhage. No significant differences were found in the incidence of such technical problems between the early and late surgical groups. If differences in outcome occur between comparable groups of patients operated early and late after aneurysm rupture, factors other than surgical technical complications may be responsible.