The authors present a series of 1767 patients with aneurysms of the vertebrobasilar circulation, most of whom were operated on 14 days or more following their last subarachnoid hemorrhage (SAH). Since 1970, 206 patients with vertebrobasilar aneurysms have been surgically treated within 7 days after their last SAH (day of SAH = Day 0). Of patients with a good preoperative grade (Botterell Grade 1 or 2), a good or excellent outcome was obtained in 80% during the first postsurgical month, irrespective of the timing of surgery. All except one of the Grade 5 patients died, and 70% of the Grade 4 patients were significantly disabled or dead. The overall operative mortality rate was the same whether surgery took place in the 1st week after SAH or was delayed. The frequency of rupture of the aneurysm during early surgery was not higher than during late surgery. Thirteen percent of patients developed a delayed ischemic neurological deficit as a consequence of reactive arterial narrowing (vasospasm). The authors recommend early surgery for patients with a good preoperative grade, whose aneurysm does not present a particular technical difficulty because of size, configuration, or location, and occasionally in patients whose lives appear to be in jeopardy because of recurrent hemorrhage.