FAP is an inherited susceptibility to diffuse colorectal adenomas and colorectal carcinoma, occurring in close to 100% of unresected colons. It is caused by a germline mutation in the Adenomatous Polyposis Coli (APC) gene located in the long arm of chromosome 5. To prevent cancer development it is recommended that patients with FAP undergo colectomy with ileo-anal or ileo-rectal anastomosis (or colectomy and end-ileostomy) at a socially convenient time before polyp progression to malignancy and before the age of 25. Patients with the attenuated FAP phenotype, often associated with mutations at the 5' terminus (exon 4 and proximally), have fewer polyps and may often delay colectomy. Patients with an ileo-rectal anastomosis are still susceptible to polyp formation in the remaining rectal stump and require 6 monthly check-ups with a flexible sigmoidoscope with removal of any polyps that develop. Therefore, an effective chemopreventative agent with a favourable side-effect profile would be of benefit to FAP patients with ileo-rectal anastomosis (IRA) and recurrent rectal polyps in addition to young adults who prefer to delay colectomy. If such an agent were to be effective in FAP patients in the prevention of colonic polyps, it may also be of benefit to the larger population of patients with sporadic colorectal adenomatous polyps who are also at risk of colorectal cancer.