A total of 216 patients with a ruptured aneurysm of the anterior part of the circle of Willis were enrolled into this prospective randomized study of timing of the operation after aneurysmal subarachnoid hemorrhage (SAH). Only patients in clinical Grades I to III (according to the classification of Hunt and Hess) who were admitted and randomly assigned to a treatment group within 72 hours after the SAH were included in the trial. The patients were randomly assigned to one of three operation groups: acute surgery (AS: 0 to 3 days after the SAH; day of SAH = Day 0), intermediate surgery (IS: 4 to 7 days after the SAH), or late surgery (LS: 8 days to an indefinite time after the SAH). Three patients (4.3%) in the IS group and six patients (8.6%) in the LS group died before surgery was undertaken. At 3 months post-SAH, 65 patients (91.5%) from the AS group were classified as independent compared to 55 (78.6%) from the IS group and 56 (80.0%) from the LS group. The management mortality rate in the AS group was 5.6% compared to 12.9% in the LS group. Of the 216 patients enrolled in the timing study, 159 were randomly assigned to an independent double-blind placebo-controlled trial of nimodipine in Grade I to III patients. A total of 79 patients received nimodipine and 80 placebo. When the nimodipine group and the no-nimodipine group (the 80 placebo-treated patients plus the 52 patients who were not entered into the nimodipine trial) were analyzed separately, a significant difference was seen in the outcome of the no-nimodipine group (dependent AS vs. dependent IS, p = 0.01). Nimodipine treatment was associated with a significant reduction of delayed ischemic deterioration (all operation group combined, nimodipine vs. no nimodipine p = 0.01; LS with nimodipine vs. LS with no nimodipine, p = 0.03).