Of 345 patients with tuberous sclerosis complex evaluated at the Mayo Clinic from 1950 to 1989, 23 were identified as having brain tumors. In 20 of the 23, histological or clinical evidence showed the tumor to be a subependymal giant cell astrocytoma. A search of the Mayo Clinic tissue registry yielded 73 giant cell-containing astrocytomas and intraventricular gliomas exclusive of ependymomas. Reexamination revealed no further examples of subependymal giant cell astrocytoma in patients without features of the tuberous sclerosis complex. Considerable histological variation was observed in the 15 subependymal giant cell astrocytomas subjected to critical microscopic review. It is of note that no correlation was noted between either the histological features, such as atypia, mitoses, endothelial proliferations, necrosis, or the flow cytometric characteristics and the clinical course or the survival time of the patients.