A 49 year old woman reported an attack of transient neurological dysfunction associated with unilateral headache. A prominent feature of the aura was a period of complete achromatopsia, so that the visual scene was experienced in monochrome. The episode developed to include features of prosopagnosia and spatial agnosia before resolving completely. Other episodes of transient neurological dysfunction followed at regular intervals until prophylactic antimigrainous therapy was initiated. Four vessel cerebral angiography and MRI of the brain were normal. Possible causes of this unusual migrainous aura are discussed with reference to current concepts of cerebral localisation.