A 17-year-old Quarter Horse mare was evaluated for colic of 24-hour duration. Clinical signs and diagnostic evaluation were consistent with duodenitis-proximal jejunitis. The horse's clinical condition deteriorated despite medical treatment and was euthanized. Aerobic culture collected from small intestinal ingesta was positive for Salmonella enterica subsp. enterica serovar Hadar. Salmonella sp. is commonly implicated in nosocomial infections in equine veterinary hospitals usually through feces containing the organism. Considering Salmonella sp. was cultured from the jejunal luminal contents and the large volume of nasogastric reflux that was evacuated in this case, a perceived risk of Salmonella sp. transmission from infected gastric reflux to other hospitalized cases was realized. Infectious agent biosecurity precautions should be undertaken in horses with nasogastric reflux to prevent hospital-acquired transmission.