The authors describe what is, to their knowledge, the first reported case of the anomalous origin of an internal carotid artery from the pulmonary artery. An otherwise asymptomatic 6-year-old girl, who presented with headaches and hypertension, underwent a comprehensive workup that revealed extensive meningeal and cerebral artery anastomoses to the left internal carotid artery--itself arising from the origin of the left pulmonary artery. This unique anatomical anomaly, caused by a disturbed pattern of aortic arch regression, resulted in a right-to-left vascular shunt into the pulmonary artery and a disturbance of intracranial artery flow patterns, complicating the management options.