Unidentified viral disease with high mortalities has been recorded consistently since 1998 in cultured carp Cyprinus carpio in Korea. In the present study, we investigated the histopathological characteristics of the diseased carp to evaluate the relatedness to koi herpesvirus disease (KHVD). Histopathogical examination revealed severe necrotic changes and vacuous cells in the kidney, spleen, liver, pancreas, heart and intestine, but eosinophilic intranuclear inclusion, a typical characteristic of KHV infection was not detected. These results suggest that KHVD may be not a cause for the high mortality occurring among cultured carp in Korea and possibly other unknown viral disease could are related.