The Irkutsk opisthorchiasis focus is analysed. Mollusс Opisthorchophorus hispanicus inhabits in the basin of Biryusa river in Taishet district of Irkutsk Region. They are potential first intermediate hosts of Opisthorchis felineus. Previously this species was related to Bithynia inflata. O. felineus was not found in examined molluscs. In the water reservoirs of Novosibirsk region there are molluscs Bithynia troscheli and B. tentaculata. They are the first intermediate hosts of O. felineus. Now investigators don’t have single opinion about genus and species status in different opisthorchiasis foci. Dace, roach and bream are second intermediate hosts of O. felineus. Dace and bream have maximum rate of infection by metacercaria of O. felineus. According to modern data human and cat are definitive hosts in Irkutsk opisthorchiasis foci. Irkutsk opisthorchiasis focus is little-studied so long as now we have only some fragmentary information about infection of mollusks, cyprinid fishes and people. That is why many questions about structure focus, its origin, quantitative characteristic, composition and distribution intermediate and definitive hosts and others until now are not investigated. Data about infection of fish and people demonstrate that opisthorchiasis problem in Irkutsk focus require great attention of scientists, practical doctors, veterinaries and inspectorate organizations. We have to admit that research works on opisthorchiasis focus evaluation in the area of Taishet are conducted without a specific program. This information is not published in the scientific journals. Now we have a rough idea about opisthorchiasis foci according to infection of cyprinids from random sampling sites. Molluscs, wild (muskrat, otter, water vole, fox and wolf) and domestic (pig and dog) mammals practically are not investigated. Especially pathogen of O. felineus and nature focus type of opisthorchiasis require regular investigations on all phases of life cycle: molluscs, fishes, piscivorous mammals, local inhabitant and also comprehensive analysis of all data and development of prophylactic steps and struggle.