Endothelin-1 (ET-1) is a potent vasoconstrictor that may play a role in cerebral vasospasm following aneurysmal subarachnoid haemorrhage (SAH). This study was planned to investigate the relationship between increased ET-1 production and cerebral vasospasm after aneurysmal SAH and to show the effect of methylprednisolone on (ET-1 ) and on the neurological condition of patients. The present study included forty patient classified into two groups; (20 patients in each group): Group A: those patients who received intracisternal methylprednisolone acetate intraoperatively and postoperatively. Group B: those patients who didn’t receive intracisternal methylprednisolone acetate. Results : Endothelin-1 serum levels were found to be decreased in patients of group A after intracisternal methylprednisolone acetate associated with clinical improvement of neurological condition. On the other hand, the level of Endothelin-1 was found to increase in group B of patients who didn’t receive intracisternal methylprednisolone acetate associated with deterioration of neurological condition.