A five year old Standardbred gelding presented to Cornell University's Equine and Farm Animal Hospital for evaluation of suspected laminitis, edema of the distal limbs, and pipestream diarrhea. Subsequent diagnostic tests revealed infection with Neorickettsia risticii, the causative organism of Potomac Horse Fever. The horse recovered with intensive treatment, and was discharged with a guarded prognosis due to chronic laminitis. Potomac Horse Fever is caused by Neorickettsia risticii, a gram negative coccus. Trematodes that utilize fresh water snails and aquatic insects as intermediate hosts are involved in the transmission of the disease. Clinical signs caused by Potomac Horse Fever include fever, diarrhea, endotoxemia, and laminitis. Prevention is difficult due to a poorly efficacious vaccine, and treatment of choice is oxytetracycline intravenously, along with symptomatic care. Fatalities are associated with subsequent endotoxemia and laminitis, as well as with the primary disease.