Improved surveillance indicates that Lyme borreliosis, an emerging zoonosis in the United Kingdom, has increased from 0.06/100,000 during 1986-1992 to 0.32/100,000 since 1996. Case reports peaked in the third quarter of each year. Several high-incidence localities were identified. Erythema migrans was reported in 41% of patients; arthritis in 4%; musculoskeletal symptoms in 18%; and neuroborreliosis in 15%.