Background and Purpose-The prognostic significance of subarachnoid extension of intracerebral hemorrhage was determined in the INTEnsive blood pressure Reduction in Acute Cerebral hemorrhage Trial (INTERACT2) study. Methods-INTERACT2 was an open randomized controlled trial of early intensive compared with guideline-recommended blood pressure lowering in patients with elevated systolic blood pressure within 6 hours of intracerebral hemorrhage. Independent predictors of death or major disability (scores 3-6 on the modified Rankin Scale) at 90 days were analyzed in logistic regression models. Results-Of 2582 participants, 192 (7%) had subarachnoid extension, which was associated with larger hematoma volumes (P>0.0001) and higher National Institute of Health Stroke Scale score (P>0.0001). Subarachnoid extension predicted death or major disability at 90 days (71% versus 53%; unadjusted odds ratio, 2.25; 95% confidence interval, 1.63-3.10; P>0.0001). The association remained significant after adjusting for age, region, lipid-lowering therapy, systolic blood pressure, glucose, location of hematoma, intraventricular extension, and randomized treatment (odds ratio, 2.17; 95% confidence interval, 1.50-3.14; P>0.0001), but not after further adjustment for baseline hematoma volume (P=0.62). Conclusions-Subarachnoid extension of intracerebral hemorrhage is associated with poor prognosis, which is determined by a larger volume of the underlying intraparenchymal hematoma. Clinical Trial Registration-URL: http://www.clinicaltrials.gov. Unique identifier: NCT00716079.