The study involved 30-135 g carp more than one year old, that had been cultured since the stage of summer fry at the Fisheries Research Station operated by the Agricultural University's Department of Aquaculture, University of Szczecin and located in a Dolna Odra power station cooling water canal. The fish selected for analyses showed the following clinical signs in summer: apathy; strong necrotic patches on gills; lustreless and rough skin with numerous deep necrotic spots extending down to the muscles; deposits of thick mucus under the gill covers. On the 4th of June 2004, three carp samples of 15 individuals each were delivered live to the German National Reference Laboratory Insel Riems for analyses. Koi herpesvirus was detected in two out of the three samples using different PCR assays. The PCR results were confirmed by nested PCR and in situ hybridization. Assays were performed on gills, brain, and kidney tissues. Samples were also taken from outbreak survivors showing no clinical signs of disease in autumn 2004 and tested by PCR and nested PCR. These results were also confirmed by in situ hybridization using different probes. This is the first detection, virus isolation and confirmation of KHV in Poland.