We report the case of a 44-year-old woman, who experienced acute back pains, leg paraesthesia, and diplopia. Analysis of the cerebrospinal fluid revealed, in addition to increased protein and decreased glucose levels, an elevated number of large atypical cells, resembling lymphoma cells. Magnetic resonance imaging of the brain and spine was normal. High levels of antibodies against Borrelia burgdorferi were found in both serum and cerebrospinal fluid. The patient completely recovered with ceftriaxone therapy.