This report describes an anaplastic oligodendroglioma in a red deer, extending from the cerebellum and anterior medulla along the dorsal part of the brain stem to the posterior cerebral hemispheres and infiltrating the meninges. Immunohistologically, the tumour cells were labelled for S-100 but were negative for glial fibrillary acidic protein, vimentin and synaptophysin. This would appear to be the first report of an oligodendroglioma in a deer.