Thoracolumbar intervertebral disk disease (IVDD) is a common, important cause of paraspinal hyperesthesia, pelvic limb ataxia, paraparesis, paraplegia, and urinary and fecal incontinence in dogs. A companion article reviewed pathophysiology, epidemiology, physical examination, and emergency medical therapy. This article addresses the diagnosis, prognosis, and treatment of dogs with thoracolumbar IVDD.