A one-year-old spayed female mixed-breed dog was referred to the Cornell University Hospital for Animals for evaluation of persistent vomiting, anorexia, and peritoneal effusion three days after jejunal resection and anastomosis for removal of a foreign body and intussusception. On presentation, the patient was in septic shock. Cytologic examination of peritoneal fluid revealed bacteria within neutrophils, confirming septic peritonitis. The patient underwent a second resection and anastomosis of the bowel. Postoperative supportive care included intravenous fluid therapy, antimicrobials, and vasopressors. The patient developed dehiscence of the surgical site and underwent a third resection and anastomosis. Wound revision surgery was required to treat an incisional infection. Multidrug resistant Escherichia coli and Streptococcus pseudintermedius were cultured from the peritoneal effusion. After ten days of hospitalization, the patient was discharged. Nineteen days later, she began vomiting. Abdominal ultrasonography showed evidence of intestinal perforation and a gastric wall abscess, and the patient was euthanized.