Cerebral vasospasm is traditionally regarded as an important cause of delayed cerebral ischaemia which occurs after subarachnoid haemorrhage (SAH), and often leads to cerebral infarction, damaged nervous system function, and poor prognosis. However, recent studies suggest that vasospasm is not the sole cause of delayed ischaemic complications. Findings that marked reduction in the incidence of vasospasm does not lead to a reduction in delayed cerebral ischaemia or better outcomes have promoted researches on other possible mechanisms that may cause ischaemic complications. Early brain injury, cortical spreading depolarizations, microthrombosis, microvascular spasm, failure of cerebral blood flow autoregulation, cell death, blood-brain barrier disruption, and initiation of an inflammatory cascade are all associated with the incidence of delayed cerebral ischaemia.