An eight month old, male free-ranging white-tailed deer was submitted to the Southeastern Cooperative Wildlife Disease Study in Athens, GA with a history of abnormal behavior. Gross post mortem findings included diffuse hepatic fibrosis, cranioventral bronchopneumonia, and a brain abscess from which Trueperella pyogenes was cultured. Histologically, there was extensive meningoencephalitis associated with intracellular protozoal organisms. By immunohistochemical staining, the protozoal organisms were negative for Neospora caninum, Toxoplasma gondii, and Sarcocystis neurona. On genetic sequencing, the organism was most closely related to Theileria cervi. In the brain, multiple intracytoplasmic ovoid apicomplexan organisms that measured 3940nm by 2579nm with a visible conoid apparatus were observed by transmission electron microscopy. Infected cells had positive cytoplasmic immunohistochemical staining for glial fibrillary acidic protein and negative staining for neurofilament, CD3, CD79a, and CD20, supporting the histologic appearance suggestive of astrocytic origin. Theileria cervi is transmitted by the tick Amblyomma americanum. Infection with T. cervi is common in free-ranging white-tailed deer within the United States with rates of infection exceeding 50% in enzootic areas. Clinical disease is rare and typically only reported in heavily infected fawns. Mycotoxins and bovine viral diarrhea were also not detected with ancillary testing. This is the first report, to the authors’ knowledge, of T. cervi being associated with a brain abscess in a white-tailed deer.Â