An 11 year-old Arabian stallion presented to the Cornell University Equine Hospital in July 2012 for a two-day history of fever, lethargy and inappetance. The referring veterinarian treated the stallion with antibiotics, non-steroidal anti-inflammatory medications and gastroprotectants, but he became colicky and was referred for further evaluation. On presentation, the stallion was anxious, tachypneic and tachycardic. He had reduced gut sounds, dehydration, limb edema, palpable digital pulses and hyperemic mucous membrances. An abdominal ultrasound revealed a fluid-filled large colon and cecum. Bloodwork was consistent with endotoxemia and disseminated intravascular coagulation. Based on the season, clinical signs and diagnostic findings, a presumptive diagnosis of Potomac Horse Fever (PHF) was made. The stallion was aggressively treated with fluid therapy and oxytetracycline, pentoxifylline, polymyxin B, flunixin meglumine, limb cryotherapy and gastroprotection. Serology for PHF was positive. Although there were additional complications, with intensive supportive care, the stallion stabilized until he improved enough to be discharged.