In a cohort of 43 pediatric patients with newly diagnosed WHO grade 3 or 4 gliomas treated on the Children’s Oncology Group ACNS0423 study, IDH1 mutations were detected in 7 of 43 (16.3%) of children with primary malignant gliomas, and no IDH2 mutations were identified. The gene discussed is IDH1; the disease is glioma.