Sinus pericranii is a rare vascular anomaly involving an abnormal communication between the extracranial and intracranial circulations. A 3-year-old girl presented with a 2 x 2-cm, midline soft-tissue mass at the vertex. Plain skull films and CT using bone windows showed erosion of the parietal bones. MRI confirmed the clinical diagnosis by identifying communication of the vascular mass with the intracranial dural venous sinus. The advantages of MRI are discussed.