Anorectal manometry is widely used to evaluate anorectal function. Few reports have described complications resulting from this procedure. A 47-year-old male underwent preoperative chemoradiotherapy and a low anterior resection for rectal cancer. The patient underwent anorectal manometry at postoperative 8 months. A rectal perforation was diagnosed shortly thereafter. The patient was initially managed conservatively using percutaneous drainage and parenteral antibiotics and then discharged on day 60 after the event. One month later, a colo-cutaneous fistula and expanding abdominal fasciitis developed. The patient underwent surgical exploration, drainage, resection of the rectum including the fistula, and redo-coloanal anastomosis with a diverting ileostomy. The patient discharged without complications on postoperative day 25. Anorectal manometry should be performed with particular care in patients who have undergone radiotherapy and anastomosis at the rectum.