Abstract Background: Rupture of an intracranial aneurysm carries a high risk of disability or death. Cerebral vasospasm remains the most troublesome complication of acute Subarachinoid-haemorraghe (SAH). Activation of the systemic immune response, manifested by increased levels of circulating cy-tokines, is believed to have a significant role in the pathogenesis of cerebrovascular vasospasm. Aim of Study: The aim of this study is to correlatebetween level of CRP and incidence of vasospasm in spontaneous S.A.H, and being an independent predictor for prognosis. Patients and Methods: Cross sectional study with stratified random sample of 30 patients who admitted in Intensive Care Unit, Neurosurgery Department, Emergency and Trauma Unit at Kasr Al-Ainy, Cairo University Hospitals, from September 2018 till April 2019 diagnosed with spontaneous Subarachnoid hemorrhage and screened for CRP. Results: Out of the 30 included in the study 10 patients (33.3%) diagnosed to have anterior communicating artery aneurysm; 2 patients (6.7%) have basilar tip aneurysm, 2 patients (6.7%) have posterior communicating artery aneurysm, 2 patients (6.7%) have posterior cerebral aneurysm, and 1 patient (1.9%) have middle cerebral artery aneurysm, 2 patient have AVM, 11 patient have no underlying pathology in the conventional 4 vessels angiography. Overall age ranged from 21 years to 80 years with a mean age 53.19 patients (63.3%) were males and 11 patients (36.7%) were females. Out from 30 patients, 14 patients (46.7%) had vasospasm, and 16 (53.3%) patients didn't have vasospasm, out of 14 patients who developed vasospasm, 13 patients (92%) initially had high serum CRP level above 50mg/L, and all patient who had rising CRP level (double to triple folds) had poor outcome. Conclusion: Vasospasm is a serious event complicating spontaneous aneurysmal subarachnoid hemorrhage, it could be diagnosed clinically or radiologically, serum CRP level is an indicator of cerebral vasospasm following aneurysmal subarachnoid hemorrhage and rising serum CRP level is an independent predictor for poor outcome.