Manifestations of the epidemic process of a parotitis infection can be explained by the theory of the self regulation of parasitic systems. A characteristic feature of epidemic parotitis is the formation of epidemic foci in the absence of parotitis cases and without the penetration of the infective agent from the outside. The epidemic wave of parotitis infection decreases as the virulence of the infective agent attenuates due to its passage through persons gaining immunity in the course of the epidemic. The avirulent infective agent persists in the body of some immune carriers till a sufficient stratum of susceptible subjects accumulates in the chain of the agent circulation. The analysis points to the autonomous character of the epidemic process not only among the urban and rural population, but also among separate social and age groups of the population within one town or settlement. The findings evidence an independent formation of the epidemic variant of the infective agent in individual schools and preschool institutions.