Ulcerative colitis (UC) is associated with an increased risk of colorectal cancer (CRC), but the risk is lower than previously estimated. In this review on the evidence of CRC risk in the UC population, we find that the effect of chemoprevention appears unproven. Surveillance should be offered in dedicated centres and restricted to subgroups with extensive disease, young age at unset, dysplastic findings or an additional diagnosis of primary sclerosing cholangitis. The use of random biopsies should be replaced by chromoendoscopy for targeting biopsies towards areas with abnormal appearance.