In recent years, extensive molecular studies have identified diagnostic and prognostic markers in gliomas that reinforce the WHO histological classification. 1p19q codeletion, O(6)-methylguanine DNA methyltransferase (MGMT) status, and mutations of isocitrate dehydrogenases 1 and 2 (IDH1/IDH2) are currently the three most pertinent markers in diffuse gliomas. Ongoing clinical trials already stratify or select patients according to their 1p19q codeletion or MGMT status. Mutations of IDH1 have been recently identified as a major prognostic factor in diffuse gliomas. Future studies should determine whether IDH1/IDH2 mutations are predictive of response to treatments. Routine use of these markers considerably contributes to a more objective classification of gliomas based on both histological and molecular features.