BACKGROUND Many clinicians allow blood pressure to run high in patients with intracranial stenosis to protect against hypoperfusion. We sought to determine whether higher blood pressure decreases the risk of stroke in these patients. RESULTS Data on 567 patients in the Warfarin-Aspirin Symptomatic Intracranial Disease (WASID) trial were analyzed. Time to ischemic stroke and stroke in the same territory of the stenotic vessel was compared in patients grouped by mean systolic blood pressure (SBP) and mean diastolic blood pressure (DBP) during the study. Additional analyses were based on severity and location of stenosis. Ischemic stroke risk increased with increasing mean SBP and DBP on univariate analysis (P<0.0001, P<0.0001) and after adjustment for risk factors (P=0.0008, P<0.0001). Elevated mean SBP and DBP also resulted in increased risk of stroke in the territory in univariate (P=0.0065, P<0.0001) and adjusted (P=0.0002, P=0.0005) analyses. The increased risk of stroke with increasing SBP was driven largely by patients in the highest SBP group. Patients with moderate (< 70%) stenosis had increased risk of stroke (P<0.0001, P=0.003) and stroke in the territory (P=0.0002, P=0.010) with increased SBP and DBP. Patients with severe (> or = 70%) stenosis had increased risk of stroke and stroke in the territory with elevated DBP (P=0.004, P=0.004). CONCLUSIONS In patients with intracranial stenosis, higher blood pressure is associated with increased (not decreased) risk of ischemic stroke and stroke in the territory of the stenotic vessel. These findings argue strongly against the common clinical practice of maintaining high blood pressure in patients with intracranial stenosis.