POSTERIOR REVERSIBLE ENCEPHALOPATHY AS THE FIRST MANIFESTATION OF GUILLAIN-BARRÉ SYNDROME. REPORT OF ONE CASE We report a 56 year old male hypertensive, who presented with a posterior reversible encephalopathy syndrome (PRES) as an initial manifestation of Guillain-Barré syndrome (GBS). His first symptoms were right hemiparesis and hemihypoesthesia, followed by headache, dizziness, dysarthria and a general feeling of discomfort. On the third day, flaccid tetraparesis, impairment of consciousness, epileptic seizures and respiratory failure appeared, along with severe hypertension. Cerebral Magnetic Resonance Imaging showed the characteristic PRES lesions. Cerebrospinal fluid analyses revealed albumin-cytological dissociation and nerve conduction studies showed an axonal demyelinating polyradiculoneuropathy, which confirmed the diagnosis of GBS. Treatment with intravenous immunoglobulin was given together with antihypertensive therapy and mechanical ventilation, achieving an important clinical and imaging remission of PRES, but maintaining tetraparesis during the hospitalization. Twelve months after discharge and regular motor rehabilitation, the patient achieved complete autonomy on the activities of daily living.  It has been postulated that the autonomic failure and the elevation of circulating pro-inflammatory cytokines in GBS may be the cause of a breach in the blood-brain barrier, thus causing PRES, that can completely remit with an adequate management.