Lyme disease is the most common vector-borne illness in the United States and is an important outpatient “hot topic” because its incidence is on the rise. In fact, Healthy People 2010 lists reduction in the incidence of Lyme disease among its public health goals for the next decade. Lyme disease is caused by the spirochete Borrelia burgdorferi. The organism is transmitted by tick vectors, which require host mammals and seasonal variation to complete the life cycle. Lyme disease remains most prevalent in areas that provide a hospitable environment for ticks and their hosts. Prompt diagnosis and treatment are vital to symptom resolution and prevention of long-term sequelae.The incidence of Lyme disease increased more than 30-fold from 1982 to 1996. In 2000, 17,730 cases were reported, representing an 8% increase from 1999. The incidence is highest in the Northeast (especially Connecticut, Rhode Island, New Jersey, New York, Delaware, Pennsylvania, Massachusetts, New Hampshire, and Vermont), the mid-Atlantic (particularly Maryland), and the Midwest (Wisconsin, Minnesota). Lyme disease has also been identified on the West Coast. There are endemic and hyperendemic counties within these states.The distribution of Lyme disease is bimodal, typically occurring in children 5 to 9 years of age and adults 50 to 59 years of age, with a slightly higher number of males affected. The majority of cases occur in June, followed by July and August. People who live and work in residential or wooded areas are at greatest risk. *160/348/5*