A nine year old girl died with a massive infarct of the right cerebral hemisphere causing transtentorial and foramen magnum herniation. The infarction was secondary to an idiopathic dissecting aneurysm. The case is unusual in that the supraclinoid segment of the right internal carotid artery, the anterior cerebral artery, and the middle cerebral artery and its three branches were embedded and sectioned longitudinally. The dissection commenced in the supraclinoid segment of the right internal carotid artery, extended into the middle and anterior cerebral arteries, and was accompanied by thrombosis of the false lumen. A literature review of 20 pediatric cases indicates the malignant natural course of the disease (76% mortality in the first two months), and emphasizes the characteristic angiographic "string sign". The diagnosis of cerebral arterial dissection during life depends on angiography and a high index of suspicion.