Lyme disease, a multisystem disorder, has now been reported to the Centers for Disease Control from 43 states of the United States. The disease is a tick-transmitted infectious disorder caused by the spirochete bacterium Borrelia burgdorferi. Lyme disease typically begins with the symptoms of flu associated with a characteristic skin rash, erythema chronicum migrans. The diagnosis of Lyme disease is best made by clinical examination and epidemiologic history, with serologic studies supporting the clinical diagnosis. Prompt diagnosis and early treatment with antibiotics will often lead to the resolution of symptoms and the prevention of late complications, Lyme carditis, neurologic manifestations, and arthritis.