This 13-month-old boy, in whom Kawasaki disease had been diagnosed at the age of 6 months, presented with subarachnoid hemorrhage caused by the rupture of a middle cerebral artery aneurysm. The authors performed an emergency craniectomy and clip occlusion of the aneurysm, which was found to be partially thrombosed. The patient was discharged 4 weeks postoperatively without apparent neurological deficit. Intracranial saccular aneurysms in the pediatric population are rare, and are occasionally associated with various systemic disorders. Kawasaki disease is a systemic vasculopathy of unknown origin, but cerebral arteries are usually spared from the disease process. This is the second case report of a ruptured cerebral aneurysm in a patient with Kawasaki disease, providing a novel clinical feature that the authors call Kawasaki syndrome.