We report the case of a 40-year-old man whose bone marrow metastases occurred 57 months after the initial diagnosis and 9 months after completing radiotherapy for an anaplastic oligodendroglioma. Four months before the demonstration of visceral metastases was obtained by bone marrow biopsy, the patient developed diffuse bone pain, pancytopenia, hypercalcemia, and panhypogammaglobulinemia. These abnormalities and other clinical signs of extracranial dissemination of the primary brain tumor were initially unrecognized until the patient was admitted with the suspicion of a nonsecretory multiple myeloma. We also briefly review the factors predisposing these tumors to spread outside the CNS, albeit rarely, and discuss the clinical implications of a misdiagnosis of extracranial invasion by anaplastic oligodendroglioma, whose chemosensitivity has been definitively demonstrated.