A 45-year-old man with diabetes mellitus and extensive congenital port-wine stains on the right side of his face (Fig. 1) had an upper respiratory tract infection for 1 week. He developed bilateral blurred vision and hyperglycemia and was admitted to hospital. Over the next week he experienced visual distortions, decreased visual acuity bilaterally, left homonymous hemianopsia, disconjugate gaze, ataxia and persistent confusion, and he then had a generalized seizure. He had no prior history of seizures, visual problems or poor school performance. His CT scan and MRI (Fig. 2) revealed mild focal encephalomalacia in the right occipital lobe with overlying leptomeningeal enhancement (A) and ipsilateral choroid plexus thickening and enhancement (B) consistent with Sturge–Weber syndrome. An electroencephalogram displayed generalized paroxysmal sharp- and slow-wave activity bilaterally, greater on the right side. Neuro-ophthalmological examination revealed a left homonymous hemianopsia, farsightedness in the left eye and an increased cup-to-disc ratio indicating chronic open-angle glaucoma in the right eye. He was given timolol eye drops in his right eye, glasses for his farsightedness and phenytoin. He had no further seizures and was discharged home. At follow-up 3 months later, his left homonymous hemianopsia had resolved.