Human Clostridium difficile-associated disease (CDAD) is of unquestioned importance in humans, and has been a not-uncommon cause of enteric disease in horses, dogs, and ratites. Over the past 5 years, C. difficile has emerged as a major cause of neonatal enteritis in pigs. Piglets 1-7 days of age are affected, with gross lesions frequently including mesocolonic edema. Colonic contents may be pasty-to-watery and yellow, although some piglets are constipated or obstipated. Focal suppuration and segmental necrosis are seen on microscopic examination of cecal and colonic lamina propria, and exudation of neutrophils and fibrin into the lumen gives rise to the so-called volcano lesions. Results of one study revealed that more than one-third of piglets with enteritis were affected by C. difficile alone, while an additional quarter of affected piglets may have had mixed infections. C. difficile may be the most important uncontrolled cause of neonatal diarrhea in pigs.