The authors present what is believed to be the first description of an intracranial arterial aneurysm attributable to birth trauma. A male neonate, the product of a precipitious, instrumented, footling breech delivery, exhibited seizures at the age of 18 hours. A computerized tomography scan of the head showed hemorrhage along the tentorium with a globular component at the incisura. Transfontanel Doppler ultrasound examination detected pulsatile arterial flow within the globular mass. Cerebral angiography demonstrated a 1.5-cm saccular aneurysm arising from a small distal branch of the superior cerebellar artery. The pathogenesis of aneurysms in children is obscure and controversial. Birth trauma may be responsible for some pediatric aneurysms that are currently classified as idiopathic or congenital, particularly aneurysms in the region of the tentorial incisura.