A ruptured aneurysm at the bifurcation of the left middle cerebral artery with an infra- optic course of the bilateral anterior cerebral arteries was found in a 28-year-old woman. Both abnormal anterior cerebral arteries arose from the ipsilateral internal carotid arteries, at the level of the origin of ophtha lmic arteries, passed underneath the ipsilateral optic nerves and turned upward at the ventral portion of the optic chiasm. In addition, an aortic coarctation was found with the use of thoracic aortography. An infra-optic course of the bilateral anterior cerebral arteries is an extremely rare anomaly. An infra-optic course of the bilateral anterior cerebral arteries is frequently associated with cerebral aneurysms and possibly with a coarctation aorta. The clinical features, radiological findings and possible genesis of this anomaly are presented.