Background and Purpose: Systemic inflammation is recognized as a hallmark of stroke. We aimed to evaluate the prognostic value of various inflammatory factors using blood at admission in patients with aneurysmal subarachnoid hemorrhage. Methods: In a multicenter observational study of patients with aneurysmal subarachnoid hemorrhage, the counts of neutrophil, platelet, and lymphocyte were collected on admission. Patients were stratified based on neutrophil counts with propensity score matching to minimize confounding. We calculated the adjusted odds ratios with 95% CIs for the primary outcome of in-hospital mortality and hospital-acquired infections. Results: A total of 6041 patients were included in this study and 344(5.7%) of them died in hospital. Propensity score matching analyses indicated that compared with the lower neutrophil counts, higher neutrophil counts were associated with increased risk of in-hospital mortality (odds ratio, 1.53 [95% CI, 1.14–2.06]), hospital-acquired infections (odds ratio, 1.61 [95% CI, 1.38–1.79]), and delayed neurological ischemic deficits (odds ratio, 1.52 [95% CI, 1.09–1.97]). Moreover, out of all the inflammatory factors studied, neutrophil counts demonstrated the highest correlation with in-hospital mortality and hospital-acquired infections. Conclusions: Among patients with aneurysmal subarachnoid hemorrhage, high neutrophil counts at admission were associated with increased mortality and hospital-acquired infections. The neutrophil count is a simple, useful marker with prognostic value in patients with aneurysmal subarachnoid hemorrhage.