Posterior reversible encephalopathy is a rare clinical and radiological syndrome with a character type of change in the brain: vasogenic edema of the white matter, mainly in the occipital and parietal lobes, usually symmetric, which is a secondary manifestation of acute dysfunction of the posterior cerebrovascular system. The main pathophysiological mechanism of PRES is a violation of tone of cerebral vessels. Hyperactivity of sympathetic NS, oxidative stress, development of endothelial dysfunction, disorders of humoral homeostasis, particularly, interaction between a number of biochemical substances can trigger the last one. The main clinical manifestations are headache, disorders of consciousness (from somnolence to coma), visual disturbances (hemianopsia, scotoma, and cortical blindness), behavioral disorders, dizziness, nausea and vomiting, epileptic seizures. The article presents the description of clinical observation of the posterior reversible encephalopathy syndrome in a child verified by MRI-data.