Intracranial pseudoaneurysms are rare, particularly in children and adolescents. They are characterized by the presence of organizing hematoma and fibrosis without true vascular elements. Most pseudoaneurysms result from events such as major trauma or infectious illness, and the development of pseudoaneurysm without a preceding incident is rare. We here describe a patient with a large pseudoaneurysm arising in the distal middle cerebral artery. A 10-year-old boy experienced a sudden onset of headache, nausea, and vomiting followed by loss of consciousness and was referred to our medical center. Brain computed tomography showed massive subcortical hemorrhage in the left temporal lobe. Digital cerebral angiography revealed a huge aneurysmal dilatation of the distal left M1 segment of the middle cerebral artery, with delayed filling and emptying of contrast media. Surgical resection of the aneurysm with evacuation of the hematoma yielded restoration of consciousness. Although the cause of aneurysm in this case is uncertain, this type of patient is seldom encountered; its etiology and mechanisms of onset are discussed with reference to the literature.