A case of septo-optic dysplasia, presenting with focal epileptic fits in a 29 year old man, is described. Gas encephalography and CT scan demonstrated the main features of the malformation: a single ventricle overhanging a narrowed third ventricle, abnormal mass in the basal forebrain corresponding to an embryonic cyst, optic atrophy. Angiography revealed deep venous anomalies, and, in particular, absence or hypoplasia of the sinus recti.