Background and Purpose— The presumed effectiveness of induced hypertension for treating delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage is based on uncontrolled case-series only. We assessed the effect of induced hypertension on cerebral blood flow (CBF) in aneurysmal subarachnoid hemorrhage patients with delayed cerebral ischemia in a randomized clinical trial. Methods— Aneurysmal subarachnoid hemorrhage patients were randomized to induced or no induced hypertension (control group) at delayed cerebral ischemia onset. CBF was assessed, blinded for treatment allocation, with computed tomographic perfusion in standardized predefined regions at delayed cerebral ischemia onset and after 24 to 36 hours of study treatment. Mean arterial blood pressure was compared between groups (linear mixed model). The primary outcome measure was the difference in change in overall CBF (Mann–Whitney U test). Results— Mean arterial blood pressure was, on average, 12 mm Hg (95% confidence interval, 8.6–14.5) higher in the hypertension group (n=12) than in the control group (n=13). Change in overall CBF (mL/100g per s) was −8.5 (range, −42 to 30) in the control group and 0.1 (range, −31–43) in the hypertension group ( P =0.25). Conclusions— Change in overall CBF did not differ to a statistically significant extent between the groups. Based on our results, 225 to 250 patients per group are needed to find a statistically significant difference in change in overall CBF between induced hypertension and no hypertension. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT0161323.