We present a case of middle-aged woman whose health problems began 3 months after a registered tick bite in endemic area of Lyme borreliosis. First symptoms included fatigue, chills, cervical lymphadenopathy, neck pain and stiffness. Patient was afebrile. Lyme disease was excluded due to lack of erythema migrans and negative enzyme immunoassay test results for anti-Borrelia antibodies. During the next few months, her condition was getting worse and symptoms were accompanied with brain fog, dizziness, palpitations, irregular menstrual cycles, insomnia, panic attacks, headaches, and muscle aches. This led to multiple medical tests and examinations, but the diagnosis failed to be established. Finally, after occurrence of paresthesia and weakness of leg muscles, clinical diagnosis of disseminated Lyme borreliosis with nervous system involvement was suspected and antibiotic therapy was initiated. After the second dose of ceftriaxone, patient got fever and her condition worsened. However, ceftriaxone therapy was continued for a total of 5 days and was followed by 4 weeks of doxycycline therapy. Upon completion of antibiotic therapy, high specific anti-Borrelia antibodies were detected by Western blot and SeraSpot. Appearance of anti-Borrelia antibodies, in contrast to negative test results performed immediately before the therapy started, indicated seroconversion. 18 months after the therapy, patient was completely without the symptoms. This paper emphasizes importance of clinical evaluation of Lyme disease and shows a unique case of seroconversion in patient with symptoms of disseminated Lyme disease. Seroconversion was likely triggered by release of lipoproteins and other immunogenic molecules from Borrelia once the bacterial die-off began due to antibiotic therapy