Objective: Vasospasm is a common complication of aneurysmal subarachnoid hemorrhage (SAH), but its economic impact has not been studied. In this study, we estimated the incremental impact of angiographic and clinical vasospasm on inpatient costs and length of stay (LOS) in a cohort of patients hospitalized for SAH. Methods: The study cohort consisted of 198 consecutive patients who underwent either endovascular or surgical treatment for SAH at Duke University Medical Center (DUMC) from February 1999 to October 2004. Patients were divided into three subgroups: clinical (+angiographic) vasospasm (n=64), angiographic vasospasm only (n=51), and patients without vasospasm (n=83). Direct and overhead inpatient costs were obtained from the DUMC cost accounting system. Costs for physician services were assigned using 2006 Medicare reimbursement rates for North Carolina based on CPT codes billed for physician services provided to patients in the study cohort. Generalized linear regression models were applied to assess the incremental impact of vasospasm on inpatient costs and LOS while adjusting for potentially confounding variables. A counterfactual approach was applied to estimate the adjusted mean cost difference between subgroups defined by the presence or absence of vasospasm. Results: The adjusted incremental cost attributable to clinical vasospasm was $41,877, a 41% increase relative to no vasospasm (95% CI: 23-62%, p<0.0001). Angiographic vasospasm was associated with a $24,528 incremental cost, a 24% increase (95% CI: 7-44%, p=0.0043). LOS was estimated to be 6.3 days or 39% longer with clinical vasospasm (95% CI: 21-61%, p<0.0001), and 4.5 days or 28% longer with angiographic vasospasm (95% CI: 9-50%, p=0.0026) relative to no vasospasm. Higher costs related to vasospasm remained significant after adjusting for differences in LOS. Conclusion: Patients with clinical and/or angiographic vasospasm incur higher inpatient costs than those without due to longer hospital stays and receipt of higher intensity care.