In the last decade, Lyme borreliosis has emerged as a complex new infection whose distribution is worldwide. The multisystem disorder, which primarily affects the skin, joints, heart and nervous system at different stages, is caused by the tick-borne spirochaete Borrelia burgdorferi. After the first weeks of infection almost all patients have a positive antibody response to the spirochaete and serological determinations are currently the most practical laboratory aid in diagnosis. Treatment with appropriate antibiotics is usually curative.