Lyme disease, also known as Lyme borreliosis, is caused by infection with Borrelia burgdorferi sensu lato (B. burgdorferi s.l.) complex, a Gram-negative spirochaete bacterium. Infection in humans takes place through tick bites. The work-up of Lyme arthritis should include a careful history including residence in, or time spent visiting, an endemic region, previous history of tick bite(s), and erythema migrans.