We report the first known case of pouch carcinoma in a 35-year-old female patient following proctocolectomy for adenocarcinoma in ulcerative pancolitis with backwash ileitis. Pouch cancer was diagnosed 2 years after the pelvic pouch procedure, illustrating that there might be a risk of pouch cancer in such patients. Adenocarcinoma arising in an ileoanal reservoir is rare. Two other cases have been reported: both patients concerned were believed to have developed cancer in small areas of residual remaining rectal mucosa.