The article summarizes the latest knowledge about the etiology, epidemiology, pathogenesis, clinical signs, diagnostic procedures and therapy of erythema migrans (EM), a cutaneous form of Borrelia infection. The sole focus on this clinical entity is intentional since EM is the most common clinical involvement in Lyme borreliosis (LB) in the Czech Republic (CR). New genospecies from the Borrelia burgdorferi sensu lato complex, B. lusitaniae and B. spielmanii, as etiologic agents are reported. Although there are no commercial tests available yet for their detection, ticks are demonstrably infected with them in Europe and probably even in the CR. Six pathogenic genospecies circulate among vertebrates and Ixodes ricinus ticks in Europe. The transmission cycle in nature, hosts identified as reservoirs and distribution of borreliae in Europe are presented. Clinical forms of EM are described in detail including accompanying features. Types of erythema in the USA and Europe are compared. In the part on differential diagnosis, allergies, skin and infectious diseases with similar appearance on the skin as EM are mentioned. Although the diagnosis of EM is exclusively clinical and serology is not indicated, methods of direct detection and two-tier testing of antibodies are discussed. There are therapeutic recommendations concerning the choice of antibiotics available in the CR.