The diffuse gliomas with IDH mutation and 1p/19q non-codeletion are now diagnosed as “astrocytoma, IDH-mutant,” delineating them from “glioblastoma, IDH-wildtype” and “oligodendroglioma, IDH-mutant and 1p/19q codeleted” due to distinct prognostic and clinical/genetic characteristics. This evidence concerns the gene IDH1 and oligodendroglioma.