Case description - A two year old Quarter Horse mare presented for a one week history of progressive ataxia and head tilt. She had a normal temperature and normal mentation. The patient was current on vaccinations for rabies, tetanus, WNV, EEE, and WEE. Clinical findings - Neurologic exam showed intention tremors, left-sided dorsal strabismus, right-sided ear droop, ptosis, head tilt, ventromedial strabismus, and loss of menace with questionable vision. The patient’s gait was hypermetric with circumduction, toe-dragging, and stumbling. This was localized to the cerebellum, brainstem, and cerebrum. CSF cytology revealed eosinophilic pleocytosis. Treatment and outcome - The patient was treated for parasitic encephalitis, but did not respond and was euthanized. Clinical relevance - Diagnosis of parasitic encephalitis in horses is difficult. Though a diagnosis of parasitic encephalitis can be made in camelids and ruminants with an eosinophilic pleocytosis, this is a rare finding in the CSF of horses.