Lyme disease (LD) is caused by the spirochete Borrelia burgdorferi and is transmitted through the bite of Ixodes spp. ticks. CDC began LD surveillance in 1982, and the Council of State and Territorial Epidemiologists designated LD a nationally notifiable disease in 1991. This report summarizes the analysis of 40,792 cases of LD reported to CDC during 2001-2002. The results of that analysis indicate that annual LD incidence increased 40% during this period. The continued emergence of LD underscores the need for persons in areas where LD is endemic to reduce their risk for infection through integrated pest management, landscaping practices, repellent use, and prompt removal of ticks.