A case of moyamoya disease is presented. The patient is a 15-year-old white Spanish girl who had the onset of the neurological symptoms at 8 months of age with seizures, transient ischemic attacks and residual left hemiparesis. Cerebral arteriography performed at the age of 1 year revealed all the features of moyamoya disease in the territory of both carotids and in the vertebrobasilar arteries. The presence of an embryonic tentorial artery, the Bernasconi-Cassinari artery, originating from the right internal carotid artery, was disclosed at 1 year of age but did not appear in an arteriogram performed at 6 years of age and it was revisualized by magnetic resonance arteriography (MRA) performed at the age of 15 years. This finding seems to indicate a very early intrauterine onset of the disease in this case and demonstrates the superiority of MRA over conventional arteriography to discover anomalies of intracranial vessels. Administration of nicardipine, a calcium channel blocker, added to conventional antiepileptic drugs that the patient had previously taken, improved the epileptic and the neurological disease.