Controversy surroundstheriskofcolorectalcancer(CRC) in ulcerative colitis (UC). Many studies have investigated this risk and reported widely varying rates. A literature search using Medline with the explosion of references identified 194 studies. Of these, 116 met our inclusion criteria from which the number of patients and cancers detected could be extracted. Overall pooled estimates,with95%confidenceintervals(CI), of cancer prevalence and incidence were obtained using a random eVects model on either the log odds or log incidence scale, as appropriate. The overall prevalence of CRC in any UC patient, based on 116 studies, was estimated to be 3.7% (95% CI 3.2–4.2%).Of the 116 studies, 41 reported colitis duration. From these the overall incidence rate was 3/1000 person years duration (pyd), (95% CI 2/1000 to 4/1000). The overall incidence rate for any child was 6/1000 pyd (95% CI 3/1000 to 13/1000). Of the 41 studies, 19 reported results stratified into 10 year intervals of disease duration. For the first 10 years the incidence rate was 2/1000 pyd (95% CI 1/1000 to 2/1000),for the second decade the incidence rate was estimatedtobe7/1000pyd(95%CI4/1000to 12/1000), and in the third decade the incidence rate was 12/1000 pyd (95% CI 7/1000 to 19/1000). These incidence rates corresponded to cumulative probabilities of 2% by 10 years, 8% by 20 years, and 18% by 30 years. The worldwide cancer incidence rates varied geographically, being 5/1000 pyd in the USA, 4/1000 pyd in the UK, and 2/1000 pyd in Scandinavia and other countries. Over time the cancer risk has increased since 1955 but this finding was not significant (p=0.8). Using new meta-analysis techniques we determined the risk of CRC inUCbydecadeofdiseaseanddefinedthe risk in pancolitics and children. We found a non-significant increase in risk over time and estimated how risk varies with geography. 

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