Background and objective: Cerebral vasospasm is a common and serious complication of aneurysmal subarachnoid haemorrhage (SAH). Many studies have revealed a role of inflammation in the development of cerebral vasospasm. This study aimed to investigate whether topically administered dexamethasone could attenuate vasospasm in SAH patients. Methods: Paired samples were designed to compare postoperative mean middle cerebral artery velocity between treated patients and controls matched for age ( 10 years), sex, location and size (small, medium or large) of aneurysm, as well as baseline mean middle cerebral artery velocity. We enrolled ten consecutive aneurysmal SAH patients who had Hunt-Hess (HH) grade 3 and Fish grade 3 lesions and were admitted within 24 hours following the onset of SAH. These patients were treated with dexamethasone 10mg topically at the end of the operation. Each treated patient was matched with a control patient who did not receive topical dexamethasone. All controls also had HH grade 3 and Fish grade 3 SAH and were admitted within 24 hours after the onset of SAH. Serial measurements of mean middle cerebral artery velocity were performed postoperatively every day for 2 weeks. Results were analysed with the paired t-test. Results: One patient (10%) in the treated group had vasospasm, without neurological deficit, compared with four patients (40%) in the control group, one of whom had hemiplegia. Paired t-test showed that the mean middle cerebral artery velocity in controls was significantly higher than that in treated patients on days 4-14. Conclusion: Topical application of dexamethasone is a promising strategy for prevention and attenuation of vasospasm following aneurysmal SAH.