A 60-year-old female was admitted because of intermittent fever, arthralgia, itching of whole body, pretibial edema, urinary incontinence, pain of both legs and gait disturbance, after an insect bite. On admission, she had fever of 38 degrees C, and nuchal pain and stiffness. Neurological examination revealed spasticity of lower legs and increased deep tendon reflexes of all extremities. Hyperesthesia and hyperalgesia were noted on C2-4 and L5-S5 areas. Leukocyte count was 10,100/mm3 and CRP was 2+. CSF showed no pleocytosis (3/mm3, lymphocyte), but total protein (50 mg/dl) and IgG (10.5 mg/dl) were increased. On T2-weighted images of brain MRI, multiple small high signal areas were shown. The symptom improved markedly by prednisolone, but 3 months later left lateral gaze palsy appeared abruptly. A demyelinating lesion of the pons to the medulla oblongata including the left paramedian pontine reticular formation was suspected, and a corticosteroid pulse therapy was very effective. Serum titer of anti-Borrelia burgdorferi-IgG antibody by indirect immunoperoxidase method was 400 x at first and 1600 x after 3 months. Neuroborreliosis was diagnosed, but high doses of intravenous penicillin were not effective, and an immune-mediated demyelinating mechanism was probably thought to play a role in the pathogenesis of neuroborreliosis.