Posterior reversible encephalopathy syndrome (PRES) is a clinicoradiologic entity commonly associated with eclampsia, septicemia, chemotherapeutic drugs etc. Concurrent occurrence of Guillain-Barre syndrome (GBS) with PRES is a rare entity. Dysautonomia is a proposed mechanism for such occurrence. Here we present a non-diabetic, non-hypertensive 63-year-old male patient, who came with acute onset flaccid quadriparesis, developing generalized seizures, altered sensorium and raised blood pressure on fifth day of illness. Magnetic resonance imaging (MRI) of brain showed altered signal intensities involving the parieto-occipital areas suggestive of posterior reversible encephalopathy. Cerebrospinal fluid analysis showed albuminocytological dissociation, nerve conduction studies revealed demyelinating type of polyneuropathy. The patient was treated with antihypertensives and antiepileptics. After resolution of the encephalopathy, intravenous immunoglobulin (IVIg) was given. The patient recovered gradually over few months. Our case concludes GBS as independent risk factor, for PRES may be secondary to dysautonomia and physicians should be aware of such rare coexistence so that early treatment can be done to reduce the mortality and morbidity.