Use of glucocorticoids to treat humans with acute spinal cord injury (SCI) is often debated. Many studies show no substantial drug-related effect on long-term functional outcome. The present study investigated high-dose methylprednisolone sodium succinate (MPSS) as treatment for dogs with severe acute thoracolumbar SCI (with no pelvic limb movement or pain perception) caused by intervertebral disk herniation. Polyethylene glycol (PEG), a drug previously suspected to exert neuroprotective effects in dogs with SCI, was also evaluated. Dogs were treated with standard hemilaminectomy and split into 3 study groups, each receiving either MPSS, PEG, or saline placebo. Adverse events were recorded, and open field gait score and number of dogs walking were assessed at 12 weeks post-SCI. Life-threatening adverse events, open field gait scores, and number of dogs walking did not differ significantly among the 3 treatment groups.