During February 2000, two trout farms, situated in NW Greece, reported unusually high losses of hatchery reared rainbow trout fry and fingerlings. Live fish and chilled samples of diseased whole fish were delivered to a veterinary laboratory in Athens for diagnostic investigation. Infections with the fungus Ichthyophonus hoferi as well as the Gram negative bacterium Aeromonas hydrophila were diagnosed in some of the samples. However, the reported clinical signs, mortality levels, age and size of the fish and the necropsy findings suggested that IPNV might also be present. The presence of the virus was detected initially by means of a rapid ELISA test kit and later confirmed by virus isolation and identification from tissue and whole fish samples by an independent virology laboratory. In neutralization tests the virus was found to relate more closely to the A2 (formerly Sp) serotype of aquatic birnaviruses suggesting that the original source of the virus is elsewhere in Europe. This is the first published report of IPN virus affecting farmed fish in Greece.