We performed a prospective study of the type, frequency, temporal profile, and prognostic role of cerebrovascular complications in 86 adults with bacterial meningitis. Cerebral angiography was performed in 27 patients (31.4%) who had focal deficits either clinically, on cranial CT, or both, and in patients who had persistent coma without explained cause despite 3 days of antibiotic therapy. Alterations of the vessel systems, including involvement of major arteries at the base of the brain, medium-sized arteries, small vessels, and major sinuses and cortical veins, were present in 13 of the 27 patients who had angiography. Typical cerebrovascular complications were arterial narrowing of the supraclinoid portion of the internal carotid artery; vessel wall irregularities, focal dilatations, and occlusions of distal branches of the middle cerebral artery; focal abnormal parenchymal blush; and thrombosis of the sagittal superior sinus and cortical veins. Prognosis for those patients with cerebrovascular complications was unfavorable. Six patients died, one remained in a vegetative state, four were moderately or slightly disabled, and only two recovered completely. The study showed that angiographically documented cerebrovascular complications are the most frequent intracranial complications in bacterial meningitis of the adult (37.1%) and are major determinants in the prognosis of this disease.