'Malignant MCA infarction' is the term used to describe rapid neurological deterioration due to the effects of space occupying cerebral oedema following middle cerebral artery (MCA) territory stroke. Early neurological decline and symptoms such as headache and vomiting should alert the clinician to this syndrome, supported by radiological evidence of cerebral oedema and mass effect in the context of large hemispheric infarction. The prognosis is generally poor, and death usually occurs as a result of transtentorial herniation and brainstem compression. Treatment options include general measures and pharmacological agents to limit the extent of oedema, and surgical decompression to relieve the pressure effects. Until recently there has been little evidence to guide appropriate treatment, though in the last few years randomised data have been published addressing the role of surgical decompression. A pooled analysis of three European randomised controlled trials suggests that hemicraniectomy performed within 48 h significantly reduces mortality, and improves functional outcome in selected patients, and this has been reflected in recent national guidelines.