The histopathological diagnosis of diffuse gliomas often lacks the precision that is needed for tailored treatment of individual patients. Assessment of the molecular aberrations will probably allow more robust and prognostically relevant classification of these tumors. Markers that have gained a lot of interest in this respect are co-deletion of complete chromosome arms 1p and 19q, (hyper)methylation of the MGMT promoter and IDH1 mutations. The aim of this study was to assess the prognostic significance of complete 1p/19q co-deletion, MGMT promoter methylation and IDH1 mutations in patients suffering from diffuse gliomas. The presence of these molecular aberrations was investigated in a series of 561 diffuse astrocytic and oligodendroglial tumors (low grade n=110, anaplastic n=118 and glioblastoma n=333) and correlated with age at diagnosis and overall survival. Complete 1p/19q co-deletion, MGMT promoter methylation and/or IDH1 mutation generally signified a better prognosis for patients with a diffuse glioma including glioblastoma. However, in all 10 patients with a histopathological diagnosis of glioblastoma included in this study complete 1p/19q co-deletion was not associated with improved survival. Furthermore, in glioblastoma patients >50 years of age the favorable prognostic significance of IDH1 mutation and MGMT promoter methylation was absent. In conclusion, molecular diagnostics is a powerful tool to obtain prognostically relevant information for glioma patients. However, for individual patients the molecular information should be interpreted with caution and weighed in the context of parameters such as age and histopathological diagnosis.