The development of posterior reversible encephalopathy syndrome (PRES) in a patient undergoing epilepsy surgery without perioperative hypertension is uncommon. A young man having epilepsy surgery with normal blood pressures had an unexplained drop in his processed electroencephalogram (pEEG) levels intraoperatively. This alerted and prompted us to search for the cause. A postoperative electroencephalogram (EEG) confirmed a diffuse slowing of cortical waves. The intraoperative findings of pEEG, magnetic resonance imaging (MRI), and EEG postoperatively prompted a diagnosis of PRES. The patient was managed conservatively and had a full recovery. This case report highlights the role of brain electrical activity monitors in PRES.