Corynebacterium pseudotuberculosis is a common cause of external abscesses in horses. Approximately 8% of affected horses develop internal infection, which is associated with increased mortality and expense. Respiratory disease caused by C. pseudotuberculosis occurs in approximately 40% of horses that develop internal C. pseudotuberculosis infection. The lower respiratory tract may be the only organ system affected and infection can manifest as pneumonia or pleuropneumonia. Approximately half of the horses that develop C. pseudotuberculosis lower respiratory tract infection have concurrent abdominal organ involvement. The liver is the site most commonly affected, although renal and splenic involvement also occurs. Abdominal ultrasound is an important diagnostic technique to specifically identify affected abdominal organs. With early diagnosis, a high proportion of horses with internal C. pseudotuberculosis infection respond well to long-term antimicrobial therapy; however, pregnant mares are at risk for fetal loss.