Rainbow trout gastroenteritis (RTGE) is a summer enteritic syndrome affecting farmed rainbow trout which has been reported since 1992 in France, Spain, Italy, and Croatia. RTGE was first reported in the UK in the year 2000 and limited information has been available about its epidemiology since this report. Our work aims to contribute to this knowledge with a retrospective cross-sectional study devised to determine the extent and severity of RTGE in the UK as well as to identify RTGE risk factors at the site level. Eighty-four sites participated in the study, representing 88% of the 2004 rainbow trout production by weight in the UK. It was found that RTGE had been present in at least 11 (13%) of these sites from 2000 to 2005 and the total number of sites affected by RTGE per year had increased over time, with prevalence values in the sample ranging from 2.4% during the year 2000 to 8.3% during 2005. Univariable analysis of the whole dataset revealed a confounding effect of high average production, leading to stratification of all the analysis. Several management and environmental variables were significantly associated with RTGE, including higher mean production, use of a major processing plant, lower residence times, lower harvest weights, use of diploid fish, systematic vaccination, water oxygenation, the use of automatic and/or demand feeding systems and higher maximum water temperature. Also, a number of fry sources were associated with RTGE, but further analysis suggested that a common source of RTGE via fry was unlikely. None of the egg sources or feed types included in the study was associated with RTGE and production for the restocking market presented a protective association. Multivariable logistic regression identified the use of a major processing plant and lower residence time as the two variables with the strongest association with RTGE presence. Overall, the results of this study have confirmed RTGE in the UK as a major disease problem that is linked to a high productivity level and production of fish for the portion-size market. (C) 2009 Elsevier B.V. All rights reserved.