In this study, total of 12 rainbow trout (average weight 5 g) from a fish farm were examined. Clinically, the fish showed inappetite and irregular swimming. In histopathological examination, focal to diffuse acinar cell degeneration and necrosis were observed in pancreas. Immunohistochemically, IPN viral antigens appeared especially in the pancreas, liver, cardiac and skeletal muscles, and occasionally in the kidneys, spleen, stomach, intestines and gills. In Reverse transcriptase-polymerase chain reaction (RT- PCR) examination, appropriately sized product (206 bp) were amplified from tissue samples and specific signals for IPN virus were observed. Apoptosis signals TUNEL (Terminal Transferase dUTP Nick End Labeling), caspases-3, -8 and -9 positivities) indicated that apoptosis was induced both by intrinsic and extrinsic pathways in the skeleton and cardiac muscles, whereas by only intrinsic pathway in the liver, spleen, kidneys, gills, stomach and intestines. However, signals of apoptotic cell death were not clearly detected in pathogenesis of IPN in the pancreas as the main target organ. In conclusion, our results suggest that apoptosis, a cell death mechanism, could be appeared in favor of IPN virus in pathogenesis of the disease in field conditions.