BACKGROUND: Basilar artery occlusion (BAO) is associated with a high mortality rate, although cases with spontaneous favorable outcomes have recently been reported, and basilar artery stenosis (BAS) has received little consideration until now. OBJECTIVE: To study the prognostic clinical factors by testing numerous combinations of admission status characteristics of patients with brain ischemia caused by BAO or BAS. METHODS: We conducted a retrospective review from the Lausanne Stroke Registry (group 1) of patients with stroke or transient ischemic attack caused by BAS less than 50% or BAO as diagnosed by magnetic resonance angiography who were not treated by thrombolysis. Neurologic findings on admission were correlated with outcomes. We compared clinical patterns associated with poor outcomes in group 1 with those in patients with stroke who died from BAO or BAS (confirmed at autopsy) (group 2). RESULTS: Eighty-eight patients were studied. The outcomes of patients with stroke in group 1 (35/43) was poor (severe disability or death) in 54% of cases. A statistical analysis revealed that 4 factors-dysarthria, pupillary disorders, lower cranial nerve involvement, and consciousness disorders on admission-were strongly (P<.001) associated with poor outcomes. The multivariate analysis showed that the outcome was poor in 100% of cases in which consciousness disorders or the combination of the remaining 3 factors were present, whereas in the absence of these factors, a poor outcome was reported in only 11%. In 87% of the 45 patients with stroke in group 2, the same clinical patterns were present on admission. CONCLUSIONS: The prognosis of BAS greater than 50% or BAO is diverse and certain clinical characteristics seem to predict a lower risk of poor outcome. Their presence may help to decide the most suitable therapy.