This report describes a case of Theiler's disease seen in an Arabian gelding that received a plasma transfusion forty days prior to developing signs of acute hepatic failure. This is the first documented case of plasma associated serum hepatitis seen at Cornell's Equine Hospital, although there have been similar reports at other institutions. The gelding presented with acute blindness, ataxia, and encephalopathic behavior. Supportive treatment was unsuccessful, and the horse died 48 hours later. Acute hepatic necrosis was confirmed at necropsy and by histopathology. The administered plasma could not be traced back to a definitve donor, and no other cases of Theiler's disease were seen or reported during this time. This case raises awareness of a rare but potentially fatal risk factor associated with plasma transfusion and highlights the need for more research on the etiology and transmission of Theiler's disease in horses.