Sinus pericranii is a rare disorder characterized by a congenital or acquired epicranial blood-filled nodule of the scalp that is in communication with an intracranial dural sinus through dilated diploic veins of the skull. We describe two patients with sinus pericranii: a 3-year-old boy with a congenital lesion and a 3-year-old girl whose lesion appeared after head trauma. We discuss the clinical presentation, dermatologic manifestations, differential diagnosis, and management as described in the available published literature. Patients with sinus pericranii may be brought to the attention of dermatologists and dermatopathologists because of skin changes in the scalp or forehead. The diagnosis is difficult to make clinically, because the skin manifestations are highly variable and may resemble other disorders of the scalp and cranium. The potentially lethal complications including hemorrhage, infection, and air embolism warrant a high index of suspicion for sinus pericranii. (J Am Acad Dermatol 2002;46:934-41.)