The authors report malignant glioma occurring in two sibling cases. The elder brother presented with right hemiparesis and hemihypesthesia at 14-year-old. Computed tomographic (CT) scanning demonstrated a low-density area in the left frontoparietal lobe. The tumor was partially removed. Histologic diagnosis was glioblastoma multiforme. Radiation therapy was given postoperatively, but he died due to tumor recurrence 15 months after onset. The younger sister was admitted comatose due to intratumoral bleeding at 19-year-old. CT scans showed a high-density area in the right temporal lobe. The tumor was excised subtotally. Histological diagnosis was malignant astrocytoma (grade III). Radiation therapy, chemotherapy (ACNU), and immunotherapy (interferon) were given postoperatively, but she died due to recurrence 34 months after onset.