Objective : The purpose of this study is to evaluate the correlation of the ICAM-l levels in serum and CSF with cerebral vasospasm in early aneurysmal subarachnoid hemorrhage [SAH] patients. Methods : A prospective analysis was performed in thirty consecutive patients who underwent early surgery for intracranial aneurysmal SAH. The serum and CSF were obtained daily through the indwelling arterial lines and intraoperative ventriculostomy, or cisternal drain for 4 consecutive days after surgery. The ICAM-1 levels in serum and CSF samples were measured via quantitative enzyme-linked immunosorbent assay. Results : The mean concentration of serum in aneurysmal SAH patients was 207.89ng/ml compared with 132.25ng/ml in controls. The mean concentration of CSF in aneurysmal SAH patients was 76.39ng/ml compared with 3.96ng/ml in controls. There were no significant differences between serum and CSF ICAM-1 level with regards to clinical characteristics in patients with aneurysmal SAH [P>0.05]. However, CSF ICAM-1 levels increased significantly in patients with vasospasm compared with those without vasospasm [P<0.05]. Conclusion : The major result of this study shows that ICAM-1 is increased in CSF after early aneurysmal SAH and that this increase in ICAM-1 has correlation with cerebral vasospasm. Further study is needed to determine whether ICAM-1 levels may be indicator in the pathogenesis of important events leading to cerebral vasospasm.