Spring viremia of carp virus (SVCV) is an important viral pathogen of common carp Cyprinus carpio and one of only five fish pathogens listed as notifiable in the 2002 International Aquatic Animal Health Code of the Office International des Epizooties (OIE). Spring viremia is most problematic in Europe. The disease has been reported in many regions in the world but never in North America. In April 2002, an epizootic with clinical signs consistent with SVCV occurred on a fish farm on the East Coast of the United States that raises koi, a strain of common carp. A virus was isolated on epithelioma papillosum cyprini cells and subsequently demonstrated by immunocytochemistry to be SVCV. The OIE reference laboratory for SVCV (Centre for Environment, Fisheries, and Aquaculture Science, Weymouth, England) has confirmed the identity of the virus.