The authors present the case of a patient treated in the Department of Infectious Diseases at CMUJ in Cracow. The patient's full clinical picture suggested the possibility of the development of neuroborreliosis and disguised the symptoms of a developing intracranial tumor. Neuroborreliosis was suspected due to epidemiologic history (a tick bite, erythema migrans), general symptoms (fatigue, hypersomnia, apathy, dysmnesia, concentration disorders) and neurological symptoms, seropositive tests for Borrelia burgdorferi in serum and cerebrospinal fluid (IgG), increased protein concentration in cerebrospinal fluid. Owing to the fact that the serologic criteria of neuroborreliosis were not fulfilled, and other symptoms (loss of consciousness) appeared, CT was done. The CT showed the presence of a tumor in the longitudinal fissure of the brain, which, after intraoperative and histopathological examination, was defined as meningioma.