Posterior reversible encephalopathy syndrome (PRES) is a clinical syndrome of encephalopathy, headache, visual disturbance, and seizures. In most cases, symptoms present acutely or subacutely in the setting of accelerated hypertension, eclampsia, autoimmune disease, immunosuppressive treatment, or cancer chemotherapy. One essential feature of PRES is the presence of reversible cerebral vasogenic edema that has a predominantly posterior distribution on brain imaging. Atypical imaging features are commonly described, including involvement of the anterior brain or brainstem and the coexistence of ischemia or hemorrhage. In most cases, both clinical and radiological findings are reversible, although permanent imaging abnormalities and residual neurological sequelae can be seen in a minority of patients. The syndrome is thought to be caused by a breakdown of the blood-brain barrier and an extravasation of the intravascular fluid. Treatment of hypertension and seizures, and withdrawal of causative agents are the mainstays of therapy in PRES.