The histologic classification of gliomas, which is based on oligodendroglial- or astrocytic-like morphology distinguishes gliomas in astrocytic tumors (grade 1- pilocytic astrocytoma to grade 4- glioblastoma), oligodendroglial and mixed tumors (grade 2 and 3) according to cell differenciation, cellularity, nuclear atypia, mitotic activity, necrosis and microvascular proliferation. Prognosis is correlated to grade. Based on interobserver variability, the histological diagnosis is often highly subjective and should be interpreted within the context of clinical and radiological data. Newly identified good prognostic markers (1p and 19q loss in oligodendrogliomas) and new molecular techniques such as microarray may further refine the existing classification.