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Accurate prognosis for patients with anaplastic oligodendroglial gliomas is increasingly difficult to make. Characterisation of these tumours remains challenging, increasing proportions of oligodendroglial diagnoses in gliomas are reported, and no WHO 2000 grade IV exists for them, so that highly anaplastic tumours can only be grouped with glioblastoma (GBM) or with grade III oligodendroglioma, which have differing clinical behaviour. Longer survival times reported for patients with glioblastoma containing an oligodendroglial element (GBMO) suggest that a grade IV for oligodendroglial tumours might exist. In patients with anaplastic gliomas containing an oligodendroglial element, we explored whether microvascular proliferation (MVP) and necrosis were associated with shorter survival, sufficient to create a grade IV. Biopsies for 98 patients with anaplastic oligodendroglioma, anaplastic oligoastrocytoma or tumours with an oligodendroglial and GBM element, discharged 1998-2004, were identified from databases at three allied neurosurgery units. Pathology reports were reviewed for the presence of MVP and necrosis. Anaplastic oligoastrocytoma and GBMO were combined to measure the effect of an astrocytic element on survival. For anaplastic oligodendroglioma patients, median survival time was 24 months, while for anaplastic oligoastrocytoma or GBMO patients, it was 9 months. Age 60 or over (P = 0.006) and astrocytic element (P = 0.01) were the only independent predictors of survival. Patients 60 and over with an astrocytic element had 4.6 times the risk of death of patients under 60 with anaplastic oligodendroglioma. A grade IV cannot be created using necrosis or MVP since neither feature predicted survival after adjustment for age and an astrocytic element. However age and an astrocytic element were strong predictors of poorer survival in patients with anaplastic oligodendroglial tumours.