We describe the case of a patient from the emergency ophthalmic clinic who presented with sudden, bilateral visual loss, headache and dizziness. The magnetic resonance imaging (MRI) showed bilateral parieto-occipital vasogenic edema of the white and grey brain matter consistent with the diagnosis of posterior reversible encephalopathy syndrome (PRES). This is a rare cause of sudden bilateral visual loss which describes a condition with bilateral edema of primarily the white but also the grey matter. The edema is usually detectable with MRI but not always with the less sensitive computed tomography (CT). Further clinical signs may be headache, seizure, nausea, character changes and reduced consciousness. Arterial hypertension, drugs inducing hypertension or drug side effects may cause PRES but sometimes the reason remains unknown. In most cases the symptoms resolve simultaneously with the edema but may also lead to severe complications. In suspected cases of PRES the blood pressure should be measured and a MRI performed, followed by intensive care and treatment of the hypertension, other symptoms and complications.