Lyme disease is a tickborne illness caused by the spirochete Borrelia burgdorferi. In a previous report we described a decrease in the CD57 lymphocyte subset in patients with chronic Lyme disease. We have now identified a patient with chronic relapsing and remitting symptoms of Lyme disease who had decreased levels of CD57 lymphocytes over 10 years. This observation represents the longest duration of an immunologic abnormality ever documented in chronic Lyme disease. The CD57 lymphocyte subset appears to be a useful marker of longterm infection with the Lyme disease spirochete.