The authors report a case of oligodendroglioma in the septum pellucidum. A 22-year-old male presented with symptoms of headache and decreased visual acuity. Simple skull series showed calcified density near the midline. Brain C-T scan revealed huge calcified mass involving right lateral ventricle, 3rd ventricle and obstructive hydrocephalus. The authors diagnosed oligodendroglioma in operative findings and pathologic examination.