Infiltrative tumors with a presumptive glial cell of origin. Most common primary intracranial neoplasm. Only known risk factors are ionizing radiation and uncommon hereditary syndromes (neurofibromatosis, tuberous sclerosis). Infiltration along white matter pathways often prevents total resection. Imaging studies (Fig. 189-1) fail to indicate full tumor extent. Grade I tumors (pilocytic astrocytomas) are the most common tumor of childhood, typically in the cerebellum; can be cured if completely resected. Grade II astrocytomas usually present with seizures in young adults; if feasible should be surgically resected. RT is helpful and chemotherapeutic agents such as temozolomide are increasingly used. Grade III (anaplastic astrocytoma) and grade IV (glioblastoma) astrocytomas are treated similarly with maximal safe surgical resection followed by RT with concomitant temozolomide, followed by 6-12 months of adjuvant temozolomide. Median survival in glioblastoma is 12-15 months. Glioblastomas invariably recur, and treatment options include reoperation, carmustine wafer implantation, and chemotherapeutic regimens including bevacizumab. The most important adverse prognostic factors in high-grade astrocytomas are older age, histologic features of glioblastoma, poor performance status, and unresectable tumor.