Lyme disease is an infectious disease caused by spirochete Borrelia burgdorferi transmitted by Ixodid tick bite. The geographic distribution of the disease is universal, but the disease has not been identified definitely in South America yet. We report a probable case of Lyme disease in a woman, living in Jagůaré slum (São Paulo), who showed characteristics skin lesions of erythema chronicum migrans, with fever, weakness, headache, muscular pain, cough, arthralgia and sensitive radicular neuropathy in the left arm. The sequential serology made by ELISA method, using Borrelia burgdorferi whole sonicated antigen from Dr. Allen C. Steere laboratory, showed high titers of IgM antibody (1:1600). Because of the persistence of high IgM response for two months, we decided to treat the patient with tetracycline 2g/day during 10 days and the sorology became negative two months. The western blotting confirmed ELISA results showing presence of five bands (IgM). This report fulfills CDC criteria for Lyme disease diagnosis.