During this decade, Lyme borreliosis has emerged as an important health problem, especially in Europe and in the United States, and there has been an explosive growth of knowledge about this condition. The true incidence of lxodes-borne borrelial infection is probably increasing, at least in parts of the world, but the reported increase is also partly attributable to a greater recognition and awareness of this infection. This paper reviews the basic knowledge about Borrelia burgdorferi, its vectors, and its reservoirs. The tendency for Lyme borreliosis to mimic other diseases and the similarities to syphilis are described. The nomenclature of the dermatologic manifestations and the staging of the disease as a localized, disseminated, and chronic infection are summarized. The clinical manifestations, from the dermatologist's point of view, and the sometimes difficult task of diagnosis both at the clinical and laboratory level are reviewed. The dermatologic manifestations erythema migrans, secondary, multiple erythema migranslike skin lesions, borrelial lymphocytoma, and acrodermatitis chronica atrophicans may serve as helpful landmarks in the identification of Lyme borreliosis.