The authors present a case of a subependymal giant cell astrocytoma (SGCA) not associated with tuberous sclerosis. On admission, a six-year-old boy had obstructive hydrocephalus caused by a huge intraventricular tumor. Preoperative T1-weighted MR images with gadolinium showed heterogeneous enhancement of the lesion. The tumor was totally removed through a right transcortical approach with frontal craniotomy. Immunohistochemical staining for glial fibrillary acidic protein (GFAP) showed a positive reaction in some of the large tumor cells and the labeling index of MIB-1 was < 1.0%. Histological examinations revealed SGCA. He has no other evidence of tuberous sclerosis at present, but the patient in this case is an infant, so there is a possibility of his being diagnosed as tuberous sclerosis in the future. Therefore, systemic regular follow-up is recommended, even when his condition is asymptomatic.