Congenital malignant gliomas are rare brain tumors about which few reports have been published. We present the clinical course and genetic alterations in an infant with a congenital malignant glioma detected incidentally by ultrasonography at 36 weeks. The tumor occupied the right temporoparietal region, extended to the posterior fossa, and significantly compressed surrounding structures. The female infant was entirely normal without macrocrania, tense fontanel, or sucking difficulties. The tumor was subtotally resected by two-stage surgery; pathological diagnosis was anaplastic astrocytoma. Immunohistochemical staining was positive for p53 and negative for epidermal growth factor receptor. There was no O(6)-methylguanine-DNA methyltransferase (MGMT) gene promoter methylation, no 1p/19q loss of heterozygosity, and no isocitrate dehydrogenase 1 (IDH1) mutation. She underwent postoperative chemotherapy and is alive and well 12 months after surgery.