An eight-year-old, male Siberian husky cross was referred with a history of an acute onset of pelvic-limb ataxia and paraparesis. Radiography and subsequent myelography of the spine revealed an extradural compression of the spinal cord at the level of the 13th thoracic (T13) to first lumbar (L1) vertebrae. Hemilaminectomy resulted in the successful removal of an extradural cystic lesion. The morphological diagnosis based on histopathology was a synovial cyst with chondromatosis. There were no postoperative complications, and the dog's condition improved markedly. At two years postoperatively, the animal remains normal on both physical and neurological examination. To the authors' knowledge, this article is the first report of an intraspinal synovial cyst in a dog.