Restorative proctocolectomy with an ileal pouch-anal anastomosis is thought to abolish the risk of colorectal adenoma development in patients suffering from familial adenomatous polyposis. Both after mucosectomy with a handsewn anastomosis and after a double-stapled anastomosis, rectal mucosa is left behind at the anastomotic site. This carries the potential for the development of polyps and a subsequent malignancy. In our clinic, two patients recently developed an adenocarcinoma at the anastomotic site, despite a yearly follow-up endoscopy.A 40-year-old female underwent an ileal pouch-anal anastomosis with a double-stapled anastomosis in 1991. She refrained from follow-up for several years, but returned eight years postoperatively with a fistula at the anastomotic site. Biopsies revealed an adenocarcinoma infiltrating in the fistula tract T2N0M0. The patient was treated with preoperative radiotherapy (60 Gy), abdominoperineal resection, and a permanent ileostomy.A 27-year-old male underwent an ileal pouch-anal anastomosis with a double-stapled anastomosis in 1990. Because of his profession, endoscopy was performed only once every two years. Endoscopic biopsies ten years postoperatively revealed adenocarcinoma T4N0M0. The patient underwent an abdominoperineal resection with partial resection of the prostate, and a permanent ileostomy was constructed.