Koi herpesvirus (KHV) is a highly contagious viral disease that may cause significant morbidity and mortality in common carp (Cyprinus carpio) (Hedrick et al. 2000; OATA 2001). Common carp is raised as a foodfish in many countries and has also been selectively bred for the ornamental fish industry where it is known as koi. The first recognized case of KHV occurred in England in 1996. Since then other cases have been confirmed in almost all countries that culture koi and/or common carp with the exception of Australia (Hedrick et al. 2000; OATA 2001; Anonymous 2003; Pokorova et al. 2005). This information sheet is intended to inform veterinarians, biologists, fish producers and hobbyists about KHV disease.