A five-year-old female Cocker Spaniel dog was presented for a sudden onset of severe vestibular dysequilibrum. Long tract signs indicated central vestibular disease and the lesion was localized to the caudal fossa. Computed tomography demonstrated a large (20 mm x 20 mm x 12 mm), homogenous, hypoattentuating mass ventral to the cerebellum showing slight peripheral ring enhancement with intravenous contrast medium. Severe syringohydromyelia was detected in the C1 and C2 spinal cord segments. Postmortem examination found a mass filled with viscid fluid dorsal to medulla oblongata with severe compression of the overlying cerebellum. On histopathology, the mass was diagnosed as epidermoid cyst. Extensive syringohydromyelia and obstructive hydrocephalus were also identified secondary to the caudal fossa cyst.