B. Svenungsson1 and Gudrun Lindh1 (1) Dept. of Infectious Diseases, Karolinska Institute, Huddinge University Hospital, S-141 86 Huddinge, Sweden Received: 16 July 1996 Accepted: 13 January 1997 Summary Ninety-nine patients who were referred to a clinic for infectious diseases on suspicion of Lyme borreliosis and whose major symptoms were fatigue, headache, myalgia and arthralgia were studied retrospectively to find out if there was any difference in symptomatology between patients who were seropositive or seronegative toBorrelia burgdorferi. 64/82 (78%) patients remembered one or more tick bites during previous years and 32/74 (43%) patients had a history of erythema migrans. Fatigue, headache, myalgia and arthralgia occurred in 84%, 72%, 54%, and 63% of the patients, respectively. 62/99 (63%) patients had an elevated IgM and/or IgG antibody titer toB. burgdorferi. There was no difference in frequency of symptoms between seropositive and seronegative individuals. 48/99 (49%) patients were treated with antibiotics, mostly oral doxycycline. Only 50% were improved after treatment. On follow-up 2 to 4 years after the first visit, 40% of the patients had recovered completely, 31% were improved, 24% reported unaltered symptoms and four patients were impaired. There was no difference in symptoms on follow-up between seropositive or seronegative patients. It is concluded that there probably is an overdiagnosis of Lyme borreliosis and that better microbiological methods are needed to confirm active disease.