Lyme disease is caused by the spirochete Borrelia burgdorferi and is transmitted by the pinhead-sized Ixodes ticks. The illness is endemic in large areas of the continental United States. The early cutaneous manifestation, termed erythema migrans, is pictured here. It consists of an expanding annular lesion around the original tick bite. Satellite areas of involvement may also be present. Pruritus or burning may be present at the site of the lesion, and the rash may be accompanied by fever, malaise, and regional lymphadenopathy. The systemic manifestations of Lyme disease include neurologic dysfunction (e.g., Bell's palsy), cardiac conduction abnormalities, and arthritis. Early antibiotic therapy for the typical skin lesion will often prevent the development of the more serious ]and long-lasting systemic illness. Serologic testing is of some value in diagnosis but results may be negative early on, especially in the absence of neurologic or joint symptoms.