The frequency of hypertensive emergencies is declining due to widespread early treatment of less severe hypertension, with contemporary incidence rates of around 1 per cent in hypertensive subjects. Hypertensive emergencies are most common in patients with long-standing, poorly controlled chronic hypertension, often following an abrupt cessation in antihypertensive therapy. Hypertensive encephalopathy is characterized by the acute onset of lethargy, confusion, headache, visual disturbance and focal or generalized seizures. An increased susceptibility to hypertensive encephalopathy exists due to the lack of hypertension in the mother and thus a breakthrough of increased cerebral blood flow from autoregulation which may lead to cerebral oedema and seizures. The cerebellum and brainstem may also be affected, and occasionally the cerebral cortex. The posterior cerebral predilection occurs through a reduction in sympathetic innervation accompanying the basilar artery and its branches. Hypertensive encephalopathy is reversible, leading to the specific term hypertensive reversible posterior leucoencephalopathy syndrome.