Formation of a colonic J-pouch with anastomosis to the rectal stump is an accepted form of reconstruction after low anterior resection (LAR) for rectal carcinoma. It is thought this can help prevent the onset of LAR syndrome as well as improve the quality of life in the first two years following surgery. Rectovaginal fistulation is a recognised complication of this form of surgery usually occurring because of technical failure leading to inclusion of the vaginal wall into the stapled anastomosis. We present an as of yet unreported case of fistulation between the upper horizontal staple line of a colonic J-pouch-the tip of the 'J'-which was formed extracorporeally with the posterior vaginal fornix. We postulate that pelvic irradiation was partly a causative factor alongside subsequent mechanical irritation. Ultimately, surgical intervention was required, following which the patient made a full recovery. Interposition of omentum may prevent this problem.