Astroblastoma is one of the very unusual type of tumors, whose histogenesis has not been clarified. It occurs mainly among children or young adults. Astroblastoma is grossly well-demarcated, and shows histologically characteristic perivascular pseudorosettes with frequent vascular hyalinization. Perivascular pseudorosettes in astroblastoma have short and thick cytoplasmic processes and blunt-ended foot plates. A 15-yr-old girl presented with headache and diplopia for one and a half year. A well-demarcated mass, 9.7 cm in diameter, was found in the right frontal lobe in brain MRI, and it was a well-enhanced inhomogenous mass. Cystic changes of various sizes were observed inside the tumor mass as well as in the posterior part of the mass, but no peritumoral edema was found. Histologically, this mass belongs to a typical astroblastoma, and no sign of anaplastic astrocytoma, gemistocytic astrocytoma or glioblastoma was found in any part of the tumor. Immunohistochemically, the tumor cells showed diffuse strong positivity for glial fibrillary acidic protein, S-100 protein, vimentin and neuron specific enolase, and focal positivity for epithelial membrane antigen and CAM 5.2, while showing negativity for synaptophysin, neurofilament protein, pan-cytokeratin and high molecular weight keratin.