Infection by spirochete Borrelia burgdorferi is mainly observed in the United States where it has taken the name of Lyme's disease, and in Europe. Its evolution may be very extended, in several phases. A few weeks after a tick-bite, the primary lesion appears, which is a chronic migrating erythema. In the following weeks or months, in the secondary phase, nerve lesions may appear, quite similar in Europe and in the United States, and cardiac lesions, mostly seen in the United States. In the following weeks, months, or years, during the tertiary phase, articular lesions may appear, frequent in the United States, much more unusual in Europe. Several years later, chronic lesions of the central nervous system may appear, described in the United States, and chronic skin lesions such as chronic atrophying acrodermatitis sometimes associated with destructive lesions of the joints underlying the skin lesion, which are only recognized in Europe. The discovery of the spirochete in a small number of these lesions, including the latest in the evolution, permits to think that, throughout this evolution, this disease is secondary to the persistence of the germ within the body; this explains the efficacy of the penicillin treatment, including in the oldest forms of the disease. Serology is quite reliable; but it becomes positive only 2 to 4 weeks after the onset of the chronic migrating erythema: needless to say the importance of this single cutaneous lesion which enables to make the diagnosis and requires the use of a tetracycline or penicillin treatment.