Twelve cases of Lyme's disease with neurological complications are reported. Seven patients had meningoradiculitis of the Garin-Bujadoux-Bannwarth type, with facial palsy in 2 cases. In 1 case the radiculitis involved only the cauda equina. Two more patients had meningomyelitis. Of the remaining 3, 1 had subacute inflammatory polyneuritis with albumino-cytologic dissociation, 1 had probable dorsal epiduritis, and the last one developed parkinsonism and communicating hydrocephalus after an otherwise classical meningoradiculitis. Three patients recalled a tick bite but only one a cutaneous eruption. No arthritis or cardiac involvement were observed. In 2 cases the CSF contained pseudo-neoplastic cells. Severe pain was a prominent feature in most cases. Pain consistently and rapidly improved on high-dose intravenous penicillin, while other signs or symptoms (e.g. paresthesias or fatigue) often lasted several months. Parkinsonism and hydrocephalus were not influenced by penicillin, and both required specific therapy. Isolated neurological (both central and peripheral) involvement is not unusual in Lyme's disease and may give rise to a wide range of signs and symptoms. This diagnosis is to be considered even when other features of Borrelia burgdorferi infection are lacking.