Cases of nonsurgical pneumoperitoneum have rarely been reported in the veterinary literature. A thoracic source of pneumoperitoneum should be considered when the suspicion of a ruptured viscus is low based on diagnostic procedures (eg, ultrasound, computed tomography, and diagnostic peritoneal lavage), in addition to physical examination (eg, lack of fever and absence of abdominal pain) and laboratory findings (eg, absence of inflammatory leukogram).