Lyme disease (LD) is not fatal but may have serious arthritic, cardiac, or neurologic sequelae. It is caused by a spirochete bacterium carried by the black or dark brown deer tick. Deer ticks are common in the NE, upper Midwest, and CA (with cases occurring in people who spend time outdoors between May and September. The first stage (early localized LD) has the distinctive bull's eye, red macular or popular rash in 50% of cases. The rash radiates from the site of the tick bite (5 cm or larger), with some central clearing, and is usually located in the axillae, midriff, inguinal, or behind knees, with regional lymphadenopathy. Rash fades in 4 weeks; untreated individuals then may have disseminated disease with fatigue, anorexia, fever chills, joint or muscle aches. Antibiotic treatment shortens symptoms and decreased risk for sequelae.