Objective: Vertebrobasilar dolichoectasia (VBD) is a poorly understood vasculopathy. VBD may be associated with an increased likelihood of stroke and all-cause mortality. The purpose of this study was to establish predictors for clinical outcome in VBD, and better guide therapeutic medical and surgical interventions. Methods: In all, 64 adult VBD cases diagnosed by magnetic resonance angiography were retrospectively identified and prospectively followed up (4-7 years). Inclusion criteria were age 18 years or older, VBD on magnetic resonance angiography, and consent to participate. Patients with inadequate follow-up data or hemodynamically significant stenosis or occlusion of the posterior circulation were excluded. Univariate and multivariate analyses were performed with predictor modeling in 45 VBD cases. Results: Basilar artery (BA) involvement was independently associated with the transient/fixed posterior circulation dysfunction (P = .03) with an adjusted odds ratio of 4.4 (95% confidence interval = 1.2-16.1). A combination of African American ethnicity, diabetes mellitus, peripheral vascular disease, smoking, and BA involvement predicted 31% of posterior circulation dysfunction, resulting in an annual predicted likelihood of stroke of 4.4% to 7.8% in this group. Hypertension, previous anterior and posterior circulation strokes, BA involvement, and lack of previous warfarin use predicted mortality in 23% of cases, resulting in an annual likelihood of death of 3.3% to 5.8% in patients with this combination of clinical and radiologic factors. Conclusions: In patients with VBD, BA involvement increases the risk of neurologic morbidity, whereas mortality seems more predicted by classic vascular risk factors than VBD features. This study may aid in predicting annual risk of stroke recurrence or death in VBD. © 2008 National Stroke Association.