Abstract: The invention relates to an in vitro process for classifying a glioma, comprising the following steps: a. Measuring at least, from a glioma patient biological sample, the Alternative Lengthening of Telomeres (ALT) status of said glioma; b. Optionally, determining the isocitrate dehydrogenase genes mutation status (IDH status) of said glioma; c. Based on the data obtained in steps (a) and optionally (b) and, if available, on the histological grade of said glioma, classifying said glioma in one of the five following classes: oligodendroglioma-like, glioblastoma IDHwt-like, glioblastoma IDHmt-like, low-grade astrocytoma-like, and other gliomas.