This chapter discusses the case of a 51-year-old woman who was referred as an emergency with features of peritonitis following endoscopic dilatation of a stricture at an ileorectal anastomosis (IRA). She had a long history of complex Crohn's disease. The patient was admitted acutely with signs of peritonitis. She was tachycardic on admission with elevated inflammatory markers. A CT scan of her abdomen and pelvis showed the presence of free air, which was tracking in her retroperitoneal tissues. Flexible sigmoidoscopy showed a mild anorectal stricture as well as stricturing of the ileorectal anastomosis, which was balloon dilated. The CT demonstrated a large intraabdominal inflammatory mass involving the rectum and small bowel proximal to the IRA. Histology of the resected bowel and phlegmon demonstrated a moderately differentiated mucinous adenocarcinoma with tumor present at the site of the enterocutaneous fistula as well as the distal resection margins.