A 43 year old previously healthy woman presented with headache and blurred vision. Visual acuity was 20/30 in both eyes, with normal colour vision, pupil, and funduscopic examinations. Computerised threshold perimetry (fig 1) revealed a left superior and right inferior homonymous quadrantanopia. Magnetic resonance imaging (MRI) of the brain demonstrated high signal abnormality in the right temporal and left parieto-occipital lobes (fig 2). A diagnosis of multiple sclerosis (MS) was established when the patient developed recurrent neurologic dysfunction.