Comment on Eur J Gastroenterol Hepatol. 2002 Oct;14(10):1061-6. Prophylactic colectomy is an established method of bowel cancer prevention in high-risk patients such as familial adenomatosis polyposis coli (FAP) and hereditary non-polyposis colorectal cancer (HNPCC) kindreds, as well as in patients with longstanding ulcerative colitis or Crohn's disease. The decision to perform such a major procedure cannot be made lightly, and issues of timing are important. In inflammatory bowel disease (IBD), the trigger to carry out colectomy usually relates to detection of dysplasia, well recognized to be a premalignant lesion. Screening methods are aimed at detection of precursor lesions or clinically occult malignancies. In current clinical practice, such screening methods are either resource intensive (e.g. colonoscopy and biopsy) or of low sensitivity and specificity (e.g. faecal occult blood testing). We discuss the development of screening techniques based upon molecular technologies and the limitations engendered by our incomplete understanding of the natural history and molecular biology of colorectal neoplasia in IBD.