A 12-year old Thoroughbred gelding presented with a recent history of severe cough and serosanguinous frothy nasal discharge, and a more chronic history of lymphangitis. On presentation, the horse was in severe respiratory distress, characterized by dyspnea, hypoxemia, and bilaterally harsh lung sounds with cranioventral crackles. Thoracic imaging revealed a severe caudodorsal to diffuse airspace pattern with air bronchograms, most consistent with pulmonary edema. The origin of this pulmonary edema was attributed to an acute respiratory distress syndrome (ARDS), likely arising from a septicemic event from the horse’s concurrent lymphangitis. This report describes the diagnosis and treatment of ARDS in this adult horse, as well as the general clinical history, pathophysiology, progression and prognosis for ARDS in equine veterinary patients.