Delayed cerebral ischemia (DCI) is common after subarachnoid hemorrhage (SAH), and often leads to cerebral infarction and poor neurological outcome. In the past, it was believed that DCI was mainly caused by cerebral vasospasm, but recent clinical trials have failed to confirm this hypothesis, and suggest that DCI has multiple pathophysiological mechanisms. This article reviews the roles of cerebral vascular dysregulation and microthrombosis in DCI after SAH.