It has been shown that thrombolytic therapy can improve clinical outcome in some patients with acute cerebral ischemia. These patients have been reported to be characterized by certain clinical and imaging findings, mainly with non-contrast enhanced computed tomography (CT). Our purpose in this study was to find out whether CT angiography (CTA) information about the status of the cerebral vessels is helpful in the selection of patients who may benefit the most from thrombolytic therapy for acvte cerebral ischemia. CTA was prospectively performed in 15 consecutive patients (6 women and 9 men; age range 44-83 years) with moderate or severe symptoms of hyperacute cerebral ischemia. The clinical manifestations of the patient's condition and the findings on CTA were analyzed. Three-dimensionally reconstructed CTA images of diagnostic quality could be obtained for all 15 patients. Of the 15 patients 14 had a vessel occlusion identified on CTA, which was consistent with and/or helpful for making the clinical diagnosis in all 14 cases; one patient had an aneurysm of the anterior communicating artery without detectable hemorrhage on CTA. Although a thrombolytic agent was not given because of CTA evidence of intracranial aneurysm, the patient nevertheless developed a massive subarachnoid hemorrhage during hospitalization. Ischemic symptoms reversed after CTA and before the initiation of thrombolytic therapy in 2 patients whose CTAs showed occlusion of secondary branch of the middle cerebral artery (MCA). CTA can provide important information before the initiation of thrombolytic therapy. Identification both of the occluded vessel and of an intracranial aneurysm is feasible with the use of CTA, which is particularly important if the intracranial aneurysm is a potential contraindication to thrombolytic therapy. Occlusion of a secondary branch of the MCA and internal carotid artery occlusion are valuable prognostic predictors.