In 1987, follow-up studies were conducted on 72 patients who had had meningoradiculitis and encephalomyelitis (8 patients) due to Borrelia burgdorferi 5-27 years previously. These patients had not been treated with antibiotics, either during the acute disease or during the interval prior to follow-up studies. The patients had exhibited the typical symptoms of Bannwarth's syndrome during the acute phase. At the follow-up studies, 33 patients showed no, and 23 only mild, clinical residual symptoms including normal CSF findings and low-positive serum IgG borrelia antibody titres (IFT; ELISA). Three patients without sequelae exhibited persistent intrathecal secretion of oligoclonal B. burgdorferi-specific CSF IgG antibodies (Immunoblot; positive borrelia CSF IgG antibody titres). Thirteen patients exhibited mild-to-medium sequelae with persistent intrathecal formation of oligoclonal B. burgdorferi-specific CSF IgG antibodies, up to 21 years after the acute illness. This persistence can be interpreted as an "immunological scar syndrome". Our follow-up studies appear to indicate that neurological manifestations of B. burgdorferi infections are generally (with few exceptions) of a benign nature. Most patients can be classified as having been cured without antibiotic therapy. No late manifestations of chronic progressive CNS borreliosis comparable to that of neurosyphilis have been seen following acute untreated neuroborreliosis.