Koi herpesvirus (KHV) causes a highly virulent disease affecting carp, Cyprinus carpio L., and poses a serious socio-economic threat to the UK carp industry. This study aimed to determine the geographic distribution and prevalence of KHV exposed fish in England and Wales through ELISA antibody testing. Only three of the 82 farms sampled produced positive results, suggesting fish farms provide a relatively safe source of fish. Of the 71 ''high-risk'' fisheries tested, 26 were positive. All eight geographic areas within England and Wales studied had at least one KHV positive site. Twelve consignments of imported koi carp from seven S.E. Asian countries were tested for KHV antibody. Six consignments from six different countries were positive. Although a high proportion of consignments were positive, the results indicate that lower risk stocks of fish exist that could be sourced by the ornamental carp sector. The study provides evidence that KHV is widespread and prevalent in ''high-risk'' fisheries. There are, however, prospects for controlling KHV as English and Welsh farms appear to be relatively free of the virus, and in most cases fish are not moved from fisheries to other waters.Journal of fish diseases. 2010 Mar 133(3):221-30. Epub 2009 Oct 30.Taylor, N. G.Dixon, P. F.Jeffery, K. R.Peeler, E. J.Denham, K. L.Way, K.Centre for Environment, Fisheries and Aquaculture Science, Weymouth, Dorset, UK. nick.taylor@cefas.co.uk.