A 54-year-old man presented with a very rare case of radiation-induced intramedullary spinal cord anaplastic astrocytoma, which developed 37 years after radiotherapy for testicular seminoma. The patient presented with weakness and numbness of the left lower extremity that had gradually aggravated for 3 months. Magnetic resonance imaging demonstrated an intramedullary mass lesion with syringomyelia at the T9 to T12 levels. Subtotal removal of the tumor was performed using standard microsurgical technique. Histological examination revealed anaplastic astrocytoma. Although radiotherapy was seriously considered, chemotherapy was employed as adjuvant therapy considering the previous treatment. Although his neurological status improved transiently after surgery, relentless neurological decline occurred and resulted in death 9 months following surgery. Considering that subtotal removal of the tumor and chemotherapy had little influence on the quality of life and the length of survival in our case, cordectomy may be the optimum treatment for patients with radiation-induced spinal intramedullary malignant astrocytoma.