Updated project metadata. Intracranial aneurysm (IA) is a pathological dilation of the cerebral artery which has a potential to rupture leading to sub arachnoid haemorrhage (SAH). One third of the patients with aneurysmal SAH (aSAH) develop symptomatic narrowing of the blood vessels called cerebral vasospasm. The outcomes in the above clinical scenarios are variable and devastating. The study was designed to decipher the molecular mechanisms underlying the pathophysiology of intracranial aneurysm formation, its rupture and subsequent development of vasospasm at the proteomic level. The study was done in two phases – discovery phase and validation phase. We performed iTRAQ-based quantitative proteomic analysis of brain vessel tissue and serum samples in three subgroups of patients with IA and compared them with those of control group (subjects with no cerebrovascular disorder) during the discovery phase. In validation phase, dysregulated proteins of biological significance i.e. ORM1 as a biomarker for unruptured aneurysm and MMP9 as a biomarker for cerebral vasospasm were validated in larger cohort of patients.