Decompressive surgery has since long been a promising therapeutic approach for patients with acute severe brain injury at risk to develop severe brain edema. The underlying rationale of removing part of the cranium is to create space for the expanding brain to prevent secondary damage to vital brain tissue. However, until recently, randomized controlled trials that demonstrate the efficacy of decompressive surgery or benefit for outcome were missing. This has changed since the results of 3 randomized trials on hemicraniectomy in malignant infarction of the middle cerebral artery have been published in 2007. In this article, the current evidence for decompressive surgery in the treatment of cerebral ischemia, intracranial hemorrhage, traumatic brain injury, inflammatory diseases, or severe metabolic derangements is reviewed. Although there is increasing evidence for the efficacy of decompressive surgery in reducing intracranial pressure and even mortality, a critical point remains the definition of good or acceptable outcome.