On making expedition and studying the functioning of opisthorchiasis foci in the Orenburg Region, the authors have districted the region and identified 3 types of districts according to the pattern of Opisthorchis transmission: 1) areas lacking the conditions for forming an invasion foci; 2) those having all links of the focus, but lacking pathogen circulation; and 3) those having all conditions for pathogen circulation and the human beings are infected from the local infested fish--Type C. By studying opisthorchiasis in the Orenburg Region, the authors have established the rate of morbidity growth and their nonuniform distribution in this region. The findings have formed the basis of dividing the Orenburg Region by the endemicity of opisthorchiasis into 4 types of areas: non-endemic, low, moderate, and high endemic. The results of districting the region by the endemicity of areas, the nature of foci, and the social and natural factors determining an epidemiological process have formed the basis of a differential package of preventive measures against opisthorchiasis in the Orenburg Region.