A 15 year old, multiparous, American Quarter Horse mare in late pregnancy, was presented for a mass protruding from the vagina that was noticed 12 hours ago. Physical examination revealed a large, 25 x 12.5 x 12.5 cm, pink to red vaginal protrusion with moderate amounts of mucoid discharge. On transrectal palpation, it was evident that the mare was carrying a live fetus. Reminder of the physical examination was unremarkable. Vaginal prolapse was diagnosed that was manually reduced and an episioplasty procedure was performed. Mare was discharged with instructions to be monitored closely for 14 days and then re-evaluated, unless there were signs of impending parturition. Owner was instructed to seek immediate veterinary care if signs of parturition were noted. Foaling occurred without the knowledge of the owner, resulting in labial tear. Mare and a premature foal were presented at the hospital. Foal died during treatment. Mare was euthanized months later due to unrelated lameness. To authors’ knowledge, this is the first case report of a vaginal prolapse in a mare.