Introduction Echinococcus multilocularis is a widespread parasite with zoonotic potential. Carnivores are the definitive hosts and rodents the alternate hosts. There have been reports of single cases of infected European beavers (Castor fiber). Humans are accidental alternate hosts of the parasite: so-called alveolar echinococcosis is one of the most dangerous zoonotic diseases and can lead to death if not treated. Materials and Methods During a project to monitor the population of the European beaver in the province of Niederosterreich, a total of 398 European beavers were submitted for necropsy in the years 2009-2014. Tissue samples for pathohistology were taken at necropsy, fixed in 7% buffered formalin and embedded in paraffin wax. Tissue sections of 3 pm thickness were cut, mounted on glass slides and stained with haematoxylin and eosin (HE). The final diagnosis was made by PCR. Results Six (1.5 %) of the animals showed multifocal to coalescing hydatid cysts surrounded by a dense capsule in the liver. Cysts were characterized by a whitish, chambered, multifocally mineralized capsule filled with a clear liquid. Microscopically they were surrounded and separated by bands of connective tissue that extended into the hepatic parenchyma, disrupting and replacing it. Many of the parasitic cysts contained several protoscolices. Conclusions This is the first report of alveolar echinococcosis in beavers in Austria. The development of protoscolices confirms that beavers are potential alternate hosts for the parasite and may contribute to its spread. The occurrence of the parasite in animals originating from the eastern part of Austria is interesting: to date the parasite has been largely looked for in the western part of the country. The finding again highlights the importance of monitoring wildlife for the presence of diseases, especially those with zoonotic potential. The risk of infection is rising due to factors such as the steady growth of the beaver and fox populations, an overlap of habitats and a high level of contamination of the environment with vulpine faecal material containing infectious eggs.