Lyme disease is the most common tick-borne disease in the United States and Europe. Increased awareness of the clinical manifestations of the disease is needed to improve detection and treatment. In the acute and late stages, Lyme disease may be difficult to distinguish from other disease processes. The epidemiology and pathophysiology of Lyme disease are directly related to the Borrelia burgdorferi spirochete and its effects on the integumentary, neurologic, cardiac, and musculoskeletal systems. Lyme arthritis is a common clinical manifestation of Lyme disease and should be considered in the evaluation of patients with monoarticular or pauciarticular joint complaints in a geographic area in which Lyme disease is endemic. Management of Lyme arthritis involves eradication of the spirochete with antibiotics. Generally, the prognosis is excellent. Arthroscopic synovectomy is reserved for refractory cases that do not respond to antibiotics.In 1977, Steere et al1 described a mysterious arthritis epidemic that affected 39 children and 12 adults in three contiguous communities in Connecticut. The illness was characterized by recurrent attacks of asymmetric swelling and pain in large joints. The knee was the most common site of involvement. Early cases in children were misdiagnosed as juvenile rheumatoid arthritis; however, the geographic clustering of cases indicated an infectious etiology. This previously unrecognized entity was dubbed Lyme arthritis after the town of Lyme, Connecticut, where most of the first known patients lived.The initial work of Steere et al 1 pointed toward an arthropod as the likely vector of transmission of Lyme arthritis because of the geographic clustering of the affected patients in sparsely settled, heavily wooded areas along the Connecticut shore and because the peak incidence occurred during the summer months. This hypothesis was supported by the presence of an expanding skin lesion, 1 to 24 weeks before the onset of arthritis, that was similar to erythema migrans. At the time, a vector-borne illness was the suspected etiology of erythema migrans. 2 Subsequent investigations into the etiology of Lyme arthritis led to the discovery of the causative agent, Borrelia burgdorferi, a spirochetal organism that is transmitted by the Ixodes tick. 3