Chronic Lyme disease is a poorly defined diagnosis that is usually given to patients with prolonged, unexplained symptoms or with alternative medical diagnoses. Data do not support the proposition that chronic, treatment-refractory infection with Borrelia burgdorferi is responsible for the many conditions that get labeled as chronic Lyme disease. Prolonged symptoms after successful treatment of Lyme disease are uncommon, but in rare cases may be severe. Prolonged courses of antibiotics neither prevent nor ameliorate these symptoms and are associated with considerable harm.