Neuroborreliosis, a manifestation of infection with the spirochete Borellia burgdorferi, has become the most frequently recognised arthropod-borne infection of the nervous system in Europe and the USA. The best criterion of an early infection with B. burgdorferi is erythema migrans (EM), but this is present in only about 40-60% of patients with validated borreliosis. Therefore use of the duration of the disease as a classification criterion for neuroborreliosis is increasing, the chronic form being distinguished from the acute when symptoms persist for more than 6 months. The diverse manifestations of neuroborreliosis require that it be included in the differential diagnosis of many neurological disorders. In Europe, meningopolyradiculoneuritis (Bannwarth's syndrome) represents the most common manifestation of acute neuroborreliosis, with the facial nerve being affected much more frequently than the other cranial nerves. Clinical symptoms affecting the central nervous system are rarely observed and then mostly in chronic courses. By far the most common manifestation of chronic neuroborreliosis is encephalomyelitis with spastic-ataxic disturbances and a disturbance of micturition. The current diagnosis of neuroborreliosis is a clinical one, which has to be confirmed by laboratory testing. In most patients, examination of the cerebrospinal fluid (CSF) reveals lymphocytic pleocytosis, damage to the blood-CSF-barrier and an intrathecal synthesis immunoglobulin (Ig) M, IgG, and sometimes IgA. Confirmation of a borrelial infection of the nervous system requires demonstration of an intrathecal synthesis of borrelial-specific antibodies in the CSF or detection of borrelial DNA in the CSF by polymerase chain reaction (PCR). There is no generally accepted therapeutic regime for the treatment of neuroborreliosis, but recent studies have shown ceftriaxone 2 g/day and cefotaxime 6 g/day to be effective in acute and chronic courses. Penicillin G 20 mega units/day and doxycycline 200 mg/day may be suitable for uncomplicated meningopolyneuritis, without involvement of the central nervous system. The durationof treatment--at least 2 weeks in the acute forms and 3 weeks in the chronic forms of neuroborreliosis--is very important for successful treatment. Corticosteroids are recommended only for patients with severe pain that does not respond to antibiotics an analgesics.