Sinus pericranii is a rare vascular anomaly involving an abnormal communication between the extracranial and intracranial circulations. A case of frontal sinus pericranii is presented which appeared to be a posttraumatic sinus because it developed 2 years after a cranial injury. However, the presence of vascular endothelium in the pathological examination and its association with a vascular anomaly (persistent trigeminal artery) suggested a congenital origin. The lesion, pericranial blood sinuses, and bone were totally removed. The computerized tomography, angiography, and magnetic resonance imaging findings are presented. The literature is reviewed and the pathogenesis of sinus pericranii is discussed.