A case of right frontal pleomorphic xanthoastrocytoma that occurred in a 7-year-old boy is reported clinicopathologically. The patient underwent surgery on September 29, 1988. Histologic diagnosis of pleomorphic xanthoastrocytoma was made because, in addition to the unique pleomorphic histologic features, positive glial fibrillary acidic protein in immunohistochemical staining and characteristic ultrastructural features, i.e., cytoplasmic intermediate fibrils and lipid vacuoles, basal lamina, and abundant reticulin networks were demonstrated. The DNA cytofluorometric analysis of the nuclei of the tumor cells disclosed the main mode to be diploid with polyploid classes (4, 8, 16, and 32C) without any aneuploidy. Despite the presence of many pleomorphic nuclei, DNA histogram of the tumor disclosed very few DNA synthetic cells indicating a biologically inactive nature of the tumor. The patient is still alive and totally asymptomatic 20 months postoperatively.