The proportion of Lyme borreliosis seropositive residents in a number of Russia is 1-2 thousand times greater than that of officially notified patients. It is suggested that due to the ability of Lyme borreliosis to manifest in the late periods after infection, the time and chronicity of the infection, the number of officially recorded patients may significantly increase due to the manifestation of the disease in seropositive apparently healthy (at the moment of an examination) dwellers. There is evidence for that it is expedient to follow up seropositive residents and tick-bitten individuals.