We describe an unusual progression of astrocytoma into secondary glioblastoma exhibiting advanced neuronal immunophenotype. A tumor of the left frontal lobe of a 35-year-old man was diagnosed as astrocytoma. The tumor was treated by partial removal with postoperative chemoradiotherapy, followed by extensive removal of the residual regrowing tumor 5 month later. A secondary tumor was discovered and partially resected 8 years later, but the patient died 11 months following the operation due to extensive tumor progression showing subarachnoidal and intraventricular dissemination. The secondary tumor was small cell-predominant, highly proliferative tumor with an extremely high MIB-1 labeling index (80%). Unexpectedly, most of the tumor cells were positive for neuronal markers (synaptophysin and NeuN), but not for glial fibrillary acidic protein (GFAP). Retrospective examination of the original tumor revealed not only diffuse GFAP expression, but also neuronal marker expressions in small numbers of tumor cells that were hard to discriminate from the other cells on hematoxylin-eosin (HE) stain. This way of malignant progression of astrocytoma was quite unusual. Although the secondary tumor was classified as glioblastoma according to World Health Organization (WHO) classification (2000), it might be categorized into new variants of malignant glioneuronal tumors proposed recently.