A one-year-old Belgian warmblood with a previously known history of successfully repaired temporal and parietal bone fracture sustained at 14 days of age was presented for investigation of a recent, acute, and progressive four limbs ataxia. The owner reported a lack of coordination and difficulty getting up with progressing paresis two weeks prior to the presentation. Neurological examination revealed pronounced hypermetria/dysmetria in walk and trot in all four limbs. No evidence of cranial nerve deficit was observed. The horse was in good general condition with unremarkable clinical parameters. Survey lateral radiographs of the cervical spine showed moderate to severe signs of cervical malformation of the vertebral canal and articular process joints, indicating cervical stenotic myelopathy. Cervical computed tomographic (CT) myelography revealed the presence of a dorsal subarachnoid diverticulum causing significant spinal cord compression at multiple locations, with associated osteoarthrosis of the cervical articular process joints. Due to a poor prognosis and warranted surgical outcome, the owner declined further treatment, and the horse was discharged with conservative corticosteroid treatment. The patient was euthanised shortly after the initial presentation due to progressive worsening. To the author’s knowledge, CT myelography findings in a yearling with cervical subarachnoid diverticulum have not been previously published. This case illustrates the usefulness of advanced imaging techniques, such as CT myelography, in combination with static and dynamic radiography to provide a better and more accurate diagnosis.