Background: Infectious disease is a major challenge in aquaculture and poses a constraint for development of farming of new species. In 2017, Siberian sturgeon (Acipenser baerii) juveniles were imported from Italy to a Swedish farm. Due to stressful conditions, 30% died during transport and in the first days after arrival. Ten days after arrival, mortalities started to occur again. Within two months, only 5% of the juveniles were still alive. Methods: Diseased fish were transported live to the National Veterinary Institute (SVA) for necropsy and further analysis. Pathological and histopathological investigation was conducted. Virology was performed on gills and internal organs by cell culture isolation and specific PCR protocols. Results: The juveniles displayed neurological signs such as lethargy, inability to maintain upright position and erratic swimming. Body condition was low. Gills were pale. One fish had petechial hemorrhage on the abdomen and the snout. The ventricles were air-filled with, but swim bladders were deflated. One specimen had intestinal hemorrhage. Viral cell cultures were negative, but PCR of gills and internal organs detected the presence of Acipenser Iridovirus European (AcIV-E). Conclusions: AcIV-E was associated with disease and high mortality in the sturgeon juveniles. Stress probably aggravated the course of the infection.