OBJECTIVEThis article reviews and summarizes recent data on the diagnosis, prognosis, and treatment of oligodendroglial tumors.METHODSHistological criteria for optimized diagnosis and grading of oligodendroglial tumors are described and discussed. The therapeutic approaches are analyzed in light of the results of recent series.RESULTSOligodendroglial tumors may be more common than is generally thought. Perinuclear halo and “chicken-wire” pattern, although considered classic histological features of oligodendrogliomas, are unreliable as sole criteria for diagnosis. Nuclear regularity and roundness and an eccentric rim of eosinophilic cytoplasm lacking obvious cell processes are more constant features. Grading should be accomplished using a composite of radiological and histopathological relevant features. The allelic loss of chromosome arms 1p and 19q might be a marker for both chemosensitivity and longer survival after chemotherapy. Oligodendrogliomas are notably chemosensitive when compared with other gliomas. For aggressive lesions, chemotherapy should be used upfront, after surgery.CONCLUSIONOligodendrogliomas are underdiagnosed. One unfortunate implication is that a large number of patients may be receiving suboptimal care. A simplification in grading of oligodendroglioma to two grades would reduce the confusion surrounding the classification and better define prognosis and response to treatment modalities. A better definition of the so-called mixed tumor should also allow a better classification of these lesions in an intermediate prognostic class between astrocytic and oligodendroglial lesions. Loss of 1p and 19q could be used as a cytogenetic marker in assisting grading. New concepts emerging in the recent literature should help optimize the diagnosis of these lesions and reduce interobserver variability.