A case of anaplastic pleomorphic xanthoastrocytoma (PXA) in a 9-year-old girl is reported. Histological features of PXAs are cellular pleomorphism of GFAP-positive cells, with intracytoplasmic lipidic vacuoles and a reticulin network, bizarre giant cells, low mitotic activity, and lack of necrosis and of endothelial vascular proliferations. These tumors are generally reported to have a favorable postoperative course. In our case, a poor clinical prognosis and spread of the illness through the CSF was observed. Immunohistochemical features of the tumor, which were histologically anaplastic in nature, were analyzed. There were small foci of necrosis in the sections of the material obtained at the first operation and extensive necrosis in that from the second operation, although the patient had not received radiotherapy between the operations. The presence of necrosis in PXA is an uncommon and significant feature. It predicts the poor prognosis seen in this case, and therefore this report strongly supports the notion that necrosis should automatically exclude a tumor from the PXA category. The histological grade was evaluated as grade 3 (according to the WHO classification).