A 22-year old man had spastic paraparesis and cerebellar syndrome of 5 months duration. CSF showed lymphocytosis, elevated protein content, hypoglycorachia, hypochlorurachia and oligoclonal banding. CT scan and MRI were normal. Extensive laboratory procedures disclosed no bacterial, viral, fungic, parasitic or inflammatory disease. Anti-Borrelia burgdorferi antibodies were present in blood (1/4000) and in CSF (1/1024). With antibiotics (penicillin G 20 millions units per day for 10 days, followed by latamoxef 1.5 g per day for 3 months) and prednisone (50 mg per day for 2 months), the cerebellar signs disappeared, the paraparesis improved and the CSF abnormalities disappeared; blood and CSF anti-Borrelia antibody levels decreased. This case is an example of a severe form of CNS impairment by Borrelia burgdorferi. In Europe, most reports show progressive para- or tetraparesis with, sometimes, intellectual, cerebellar or cranial nerve impairment. In some cases, the signs are less diffuse or more acute. Lymphocytic meningitis is present with hyperalbuminorachia and oligoclonal banding; hypoglycorachia is mentioned in only one other report. Diagnosis is made by high blood and CSF antibody titers and demonstration of local synthesis. As in syphilis, borrelian meningoencephalomyelitis could be the third stage of the disease. Its treatment, often disappointing, consists of antibiotics (penicillin G or latamoxef) and in some cases corticosteroids.