Subependymal giant cell astrocytomas associated with tuberous sclerosis were studied with immunostains for glial fibrillary acidic protein (GFAP), myelin basic protein (MBP) and neuron-specific enolase (NSE). Tumor tissue was composed of three forms of cells; polygonal, ovoid and fusiform. A polygonal form was large in size and contained a vesicular nucleus, a distinct nucleolus and scarce Nissl granules resembling a nerve cell. An ovoid cell was similar to a gemistocytic astrocyte. Glial fibers stained with PTAH were observed to surround the tumor cell cluster. Immunocytochemically the polygonal cells were GFAP-and NSE-positive, the ovoid cells were GFAP-, MBP- and NSE-positive, and the fusiform cells were sometimes GFAP- and NSE-positive. The origin of tumor cells remains controversial, either glial or neuronal. This tumor occurs commonly in the subependymal region where germinal matrix cells appear at the early developmental stage. These results suggest that subependymal giant cell astrocytoma could have the totipotential to differentiate to astrocytic, oligodendrocytic as well as neuronal cells.